PROFICIENCY STUDY AQA 10-11 HYDROCARBONS IN SOIL by hjkuiw354

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									PROFICIENCY STUDY AQA 10-11
HYDROCARBONS IN SOIL

December 2010
                                       ACKNOWLEDGMENTS




This study was conducted by the National Measurement Institute (NMI). Support funding was
provided by the Australian Government Department of Innovation, Industry, Science and Research.
I would like to thank the management and staff of the participating laboratories for supporting the
study. It is only through widespread participation that we can provide an effective service to
laboratories.
The assistance of the following NMI staff members in the planning, conduct and reporting of the study
is acknowledged.



Geoff Morschel
Luke Baker




Paul Armishaw
Team Leader
Chemical Proficiency Testing




                                                   i
                                     TABLE OF CONTENTS
1     SUMMARY                                                         1
1     INTRODUCTION                                                   2
    1.1 NMI Proficiency Testing Program                              2
    1.2 Study Aims                                                   2
    1.3 Study Conduct                                                2
2     STUDY INFORMATION                                              2
    2.1 Selection of Hydrocarbon                                     2
    2.2 Study Timetable                                              3
    2.3 Participation                                                3
    2.4 Test Material Specification                                  3
    2.5 Laboratory Code                                              3
    2.6 Sample Preparation and Homogeneity Testing                   3
    2.7 Stability of Analytes                                        3
    2.8 Sample Storage, Dispatch and Receipt                         3
    2.9 Instructions to Participants                                 3
    2.10 Interim Report                                              4
3     PARTICIPANT LABORATORY INFORMATION                              5
4     PRESENTATION OF RESULTS AND STATISTICAL ANALYSIS               8
    4.1 Results Summary                                              8
    4.2 Assigned Value                                               8
    4.3 Between-Laboratory Coefficient of Variation                  8
    4.4 Target Standard Deviation                                    8
    4.5 z-Score                                                      9
    4.6 En-Score                                                     9
    4.7 Traceability and Measurement Uncertainty                     9
    4.8 Robust Average                                               9
5     TABLES AND FIGURES                                             10
6     DISCUSSION OF RESULTS                                          32
    6.1 Assigned Value - Total Petroleum Hydrocarbons in Sample S1   32
    6.2 Measurement Uncertainty Reported by Participants             32
    6.3 z-Score                                                      32
    6.4 En-Score                                                     32
    6.5 Participants’ Analytical Methods                             33
    6.6 Certified Reference Materials (CRM)                          34
    6.7 Comparison with Previous Proficiency Tests.                  34
7     REFERENCES                                                     35
APPENDIX 1. PARTICIPANT LABORATORIES                                 36
APPENDIX 2 - SAMPLE PREPARATION AND HOMOGENEITY TESTING              37
  A2.1 Diesel Fuel Preparation                                       37
  A2.2 Test sample Preparation                                       37
  A2.3 Homogeneity Testing                                           38
APPENDIX 3 - ROBUST AVERAGE AND ASSOCIATED UNCERTAINTY               39
APPENDIX 4 - ACRONYMS AND ABBREVIATIONS                              40


                                                ii
1      SUMMARY
Proficiency test AQA 10-11 Petroleum Hydrocarbons in Soil was conducted in September-
October 2010, 21 laboratories participated and nineteen laboratories submitted results.
Three sets of test samples were prepared at the NMI laboratory in Sydney using soil taken
from the grounds of the laboratory in Pymble.
Sample S1 was prepared from soil to which was added artificially weathered diesel fuel.
Sample S2 was prepared from soil to which was added an acetone solution of unleaded petrol
and diesel fuel. The samples were tested for homogeneity and found to be sufficiently
homogeneous for use in the study.
Participants measured total petroleum hydrocarbons (TPH) in Sample S1 and benzene,
toluene, ethylbenzene and xylenes (BTEX) in Sample S2.
The outcome of the study was assessed against the aim as follows:
i)     compare the performances of participant laboratories and to assess their proficiency in
       identifying and measuring petroleum hydrocarbon pollutants in soil.
         Laboratory performance was assessed using both z-scores and En-scores.
         Of 85 z-scores, 66 (78%) returned a satisfactory score of |z|  2.
         Of 85 En-scores, 54 (64%) returned a satisfactory score of |En|  1.
ii)    evaluate the laboratories’ test methods.
         For TPH, participants used solvent extraction using dichloromethane, acetone or
         alkane solvents, either alone or in various mixtures. Sonication, solvent extraction,
         and Accelerated Solvent Extraction (ASE) techniques were used. Three participants
         reported using a silica cleanup and two used Florisil. Sixteen participants used GC
         with FID, four used GC/MS. No trends in the reported results were evident with
         either the extraction technique or the detector used.
         For BTEX, most participants used a solvent extraction followed by purge-and-
         trap/GC/MS. A headspace technique was used by three participants.
iii)   develop the practical application of traceability and measurement uncertainty.
         Of 160 numeric results, 139 (87%) were reported with an associated expanded
         measurement uncertainty. The magnitude of these uncertainties was within the range
         1.5 – 101% relative; 115 were within what the study coordinator believes to be a
         reasonable range of 10 to 100 % relative.
         Assigned values were the consensus of participants’ results, so although expressed in
         SI units, metrological traceability of the assigned values has not been established.




                                  AQA 10-11 Hydrocarbons in Soil                                 1
1     INTRODUCTION
1.1       NMI Proficiency Testing Program
The National Measurement Institute (NMI) is responsible for Australia’s national
measurement infrastructure, providing a range of services including a chemical proficiency
testing program. Proficiency testing (PT) is: ‘evaluation of participant performance against
pre-established criteria by means of interlaboratory comparison.’1 NMI PT studies target
chemical testing in areas of high public significance such as trade, environment, law
enforcement and food safety. NMI offers studies in:
         pesticide residues in fruit and vegetables, soil and water;
         petroleum hydrocarbons in soil and water;
         metals in soil, water, food and pharmaceuticals;
         controlled drug assay;
         folic acid in flour; and
         allergens in food.
1.2       Study Aims
The aims of the study were to:
          compare the performances of participant laboratories and to assess their proficiency in
           identifying and measuring petroleum hydrocarbon pollutants in soil;
          evaluate the laboratories’ test methods; and
          develop the practical application of traceability and measurement uncertainty.
The choice of the test method was left to the participating laboratories.
1.3       Study Conduct
The conduct of NMI proficiency tests is described in the NMI Chemical Proficiency Testing
Study Protocol.2 The statistical methods used are described in the NMI Chemical Proficiency
Statistical Manual.3 These documents have been prepared with reference to ILAC-G13
guidelines4, ISO 17043-11 and The International Harmonized Protocol for Proficiency Testing
of (Chemical) Analytical Laboratories.5
NMI is accredited by the National Association of Testing Authorities, Australia (NATA) to
International Laboratory Accreditation Cooperation Guide Thirteen (ILAC-G13)4 as a
provider of proficiency testing schemes. This proficiency test is within the scope of NMI’s
accreditation.
2     STUDY INFORMATION
2.1       Selection of Hydrocarbon
The hydrocarbons studied were typical of those measured by laboratories monitoring soil to
assess the impact of transport fuels in the environment, for example in the remediation of
contaminated service station sites. Two samples were prepared, S1 representing soil
contaminated with diesel fuel and S2 representing soil contaminated with both diesel and un-
leaded petrol. The concentrations were typical of those encountered by environmental testing
laboratories. The hydrocarbons studied (>C16-C35 aliphatics) have investigation levels set in
the National Environmental Protection Council Guideline on Investigation Levels for Soil and
Groundwater.6




2                                     AQA 10-11 Hydrocarbons in Soil
Participants were asked to report TPH and also a breakdown of the hydrocarbons by chain-
length in Sample S1. They were asked to report the volatile hydrocarbons, (C6-C9, benzene,
toluene, ethylbenzene and xylenes) in sample S2.
2.2       Study Timetable
The timetable of the study was:
Invitation issued:          6 August 2010
Samples dispatched:         6 September 2010
Results due:                4 October 2010
Interim report issued:      13 October 2010
2.3       Participation
A total of fifty-seven international, national, state government and private laboratories were
invited to participate. Twenty-one laboratories agreed to participate and nineteen submitted
results. The laboratories that accepted the offer to participate are listed in Appendix 1.
2.4       Test Material Specification
Two test samples were prepared from soil taken from the grounds of the NMI Laboratories at
Pymble, NSW. Sample S1 was soil spiked with diesel fuel that had been treated to remove
volatile components so that it contained predominantly hydrocarbons in the range C10-C28.
Sample S2 was soil that had been spiked with un-leaded gasoline and the same diesel fuel
used in Sample S1.
2.5       Laboratory Code
To ensure confidentiality, all laboratories that agreed to participate were assigned a random
code number.
2.6       Sample Preparation and Homogeneity Testing
The preparation of the study samples and their testing for homogeneity is described in
Appendix 2. The study samples were demonstrated to be sufficiently homogeneous.
2.7       Stability of Analytes
The storage stability of petroleum hydrocarbons in soil stored at 4C has been previously
established.7
2.8       Sample Storage, Dispatch and Receipt
The test samples were stored in a refrigerator at approximately 4C prior to dispatch.
The samples were packaged into insulated styrene foam boxes and dispatched by courier on
6 September 2010.
The following items were also sent to participants:
    a covering letter which included a description of the test samples and instructions for
       participants; and
    a faxback form for participants to confirm the receipt and condition of the test
       samples.
An electronic results sheet was e-mailed to participants.
2.9       Instructions to Participants
Participants were instructed as follows:
          Quantitatively analyse the samples using your normal test method.



                                   AQA 10-11 Hydrocarbons in Soil                                3
       Do not test for BTEX components in sample S1.
       Report results for the following:
            o S1: Total Petroleum Hydrocarbons.
            o S2 and S3: Volatile Hydrocarbons (C6 to C9), Benzene, Toluene, Ethyl
                 benzene and Xylenes.
       Report results on the electronic results sheet emailed to you.
       No limit of reporting has been set for this study. Report results as you would report
        them to a client, applying the limit of reporting of the method used for analysis. This is
        the figure that will be used in all statistical analysis in the study report.
       Total Petroleum Hydrocarbon (TPH) concentrations in these samples are between 500
        and 10000 g /L. Individual BTEX components are between 0.5 and 200 ug/L.
       Report petroleum hydrocarbons by chain length groups and indicate the start/finish
        points for each hydrocarbon range.
       Report TPH using your laboratory’s chosen quantitation range, and indicate what this
        range is.
       For each analyte in each sample, report the analytical results in units of µg/L together
        with an associated expanded uncertainty (eg 2000  200 g/L).
       Report the basis of your uncertainty estimates (eg uncertainty budget, repeatability
        precision, long term result variability).
       If determined, report your percentage recovery. This will be presented in the report
        for information only.
       Return the completed results sheet by e-mail (paul.armishaw@measurement.gov.au),
        or if this is not possible, print and fax to +61 2 9449 0123.
       Please return completed result sheet by 4 October 2010. Late results cannot be
        included in the study report.

2.10 Interim Report
An interim report was e-mailed to participants on 13th October 2010.




4                                 AQA 10-11 Hydrocarbons in Soil
3       PARTICIPANT LABORATORY INFORMATION
                                                             Table 1 Test Methods Sample S1 TPH
Lab.      Mass
                   TPH Extraction                                                                 TPH Cleanup     Measurement
Code      (g)
1         10       Solvent - DCM/Acetone                                                          None            GC-FID
                                                                                                                  GC-FID DB-TPH column 30 m x 0.25mm id x
3         5        ASE extraction with dichloromethane after mixing with drying agent             Silica
                                                                                                                  0.25um film with 2 m retention gap
4         10       50% DCM/ Acetone                                                               Nil.            GC-FID
5         15       Soil-Liquid (Dichloromethane)                                                  N/A             GC-FID
6         2        Dichloromethane, sonication                                                    no              GCMS, HP5ms 30m x 0.25 mm x 0.25 um
7         18.254   via ISO 16703                                                                  florisil        GC-FID
                                                                                                  florisil with
8         5        DCM and sonicate for 30mins                                                                    GC-FID ZB-1 column
                                                                                                  hexane
9         30       50ml of solvent                                                                n/a             GC/FID
10        4        DCM / Acetone (1:1)                                                            none            GC-FID HP-5M3 15m X 0.32 mm X 0.5 um
11        25       Dichloromethane                                                                Silica Gel      GC-MS
                   solvent extraction for both GRO and DRO. DRO analyzed by direct injection
12        10                                                                                                      GC FID
                   and GRO by Purge and Trap
13        10       DCM/Acetone extraction using rolling and sonication                            no cleanup      GC-FID
15        10       Sonication with 1:1 20 mL dichloromethane/acetone.                             None.           HP1 column with FID detection.
                   Acetone/DCM at 50:50 for C10 plus; Headspace analysis for BTX and volatiles
16        10                                                                                      No clean up     GC-FID-FID and Headspace, GC-FID
                   (C6-C9 bracket)
17        10       Extraction with DCM:Acetone                                                    None            GC-FID using an SGE HT5 column
                   TPH (C10-C36) extracted by Accelerated Solvent Extractor (ASE) using                           Agilent 7890/5975 GC/MS. J&W capilary column:
18        10g                                                                                     Silica gel
                   DCM:acetone:hexane (1:1:1)                                                                     DB5-MSUI 30m x 0.25mm x 0.25µm.
                    solvent was added to 10g of sample, then under went a sonication extraction                   Agilent 6890N-GCFID (HP-5 30mx0.32mmx0.25um
                                                                                                  No cleanup
19        50       procedure. Extract analysed via GCFID(c10-c36) and GCMS Purge/trap (c6-                        column) /Agilent Purge+Trap GCMS (DB-VRX
                                                                                                  performed
                   c9)                                                                                            30mx0.25mmx1.4um column)
20        10       Extracted with organic solvent                                                 None            GC-FID ZB-5 30m x 0.25mm x 0.25 mm
21        15       Hexane:acetone extract                                                         Nil             GC-FID
    5




                                                                   AQA 10-11 Hydrocarbons in Soil
                                                            Table 2 Test Methods Sample S2 BTEX
        BTEX
Lab.
        Sample      BTEX Extraction                                        BTEX Measurement
Code
        Mass. (g)
1       10          Solvent - Methanol                                     GC-MS
3       5           Extract 10 ml methanol, 50 ul of extract added to      Purge and trap GCMS 30 m x 0.25mm id x 1um
                    water and analysed                                     film BP624
4       5           Sample extracted with methanol                         GC/MS purge and Trap
5       10          Soil-Liquid (Methanol), Purge and Trap Concentrator    GC-FID
6       2           Acetone, sonication                                    GCMS, HP5ms 30mx 0.25mm x 0.25um
7
8       5           Headspace Analysis                                     GC-FID ZB-35 column
9       10          20ml of solvent                                        GC/MS
10      5           Methanol extraction, followed by Purge and trap        GC-MS         HP-VOC        30m X 0.22 mm
                                                                           X 1.12 um
11      25          Dichloromethane                                        GCMS
12      10          SOLVENT EXTRACTION AND ANALYZED BY                     GC FID
                    PURGE AND TRAP
13      4           Methanol extraction                                    GC-MS with purge and trap
15      10          Sonication with 1:1 20 mL dichloromethane/acetone.     HP1 column with FID detection.
16      2           Headspace technique followed by GC-FID                 GC-FID-FID and Headspace, GC-FID
17      10          Extraction with methanol.                              GCMS using a Varian VF-624ms column.
18      0.1668      Headspace analysis                                     Agilent 7890/5975 GC/MS. SGE capilary
                                                                           column: BP1 60m x 0.32mm x 1.0µm.
19      50          surrogate was added to sample in a 40ml VOA vial.      Agilent Purge+Trap GCMS (DB-VRX
                    Internal standard was added. Sample purged and         30mx0.25mmx1.4um column)
                    trapped, then introduced into a GCMS
20      1           Purge and trap                                         GC-MSD
21
    6




                                                                   AQA 10-11 Hydrocarbons in Soil
              Table 3 Basis of Expanded Uncertainty Estimate Sample S1 TPH
Lab. Code      Basis of Uncertainty Estimate
1
3              Longterm reproducibility
4              Validation
5              The estimate is compliant with the "ISO Guide to the Uncertainty in Measurement" and is
               based on in-house validation and quality control data. A coverage factor of 2 is used to give a
               confidence level of approximately 95%.
6              2 x s.d.
7              Uncertainty budget
8              2 x standard deviation(annual average) of normal Quality control sample run with each batch
9              NATA Technical Note No 33
10             Spiked sample recoveries.
11             Standard deviation of replicate results
12
13             Repeatability Precision
15             Typical duplicates.
16             Spike recoveries
17             Validation Data
18             Uncertainty budget
19             Precision and bias from long term trends - determined in-house
20             Ongoing precision and recovery
21


                      Table 4 Additional Comment or Discussion of Results
Lab Code    Sample        Comment or Discussion
    4          S2         TPH is the sum of C10-C40.
                          The blank soil supplied contains some reportable hydrocarbons in the C15 - C 36
     10       S1          range.
     11       S2          C7-C9 reported not C6-C9
     12     S1 & S2       ALL RESULTS WERE AVERAGED

     15       S2          The TPH result for Sample S2 includes BTEX analytes and only applies to the C6-C9
                          region as requested in the "Reporting results" section of the Study Details.




                                       AQA 10-11 Hydrocarbons in Soil                                        7
4                     PRESENTATION OF RESULTS AND STATISTICAL ANALYSIS
4.1                     Results Summary
Participant results are listed in Tables 5 to 19 with resultant summary statistics: mean,
median, maximum, minimum, robust standard deviation (SDrob) and robust coefficient of
variation (CVrob).
Bar charts of results and performance scores are presented in Figures 2 to 16.
An example chart with interpretation guide is shown in Figure 1.
                                                                                                                                                     Independent estimates of analyte
                                   Histogram of distribution of results                                                                              concentration with associated uncertainties
                                   around the assigned value                                                   Assigned value and                    (coverage factor is 2).
                                   (illustrates participant consensus).                                        associated expanded                   Md = Median (of participants’ results)
                                                                                                               uncertainty (coverage factor          H.V. = Value from NMI testing
                                                                                                               is 2).                                S = Spike (formulated concentration)
                                                                                                                                                     R.A.= Robust average

                                                  8
                                                            Distr ibution of Results                                           Results: S1 - TPH
                                                                                                                                    Assigned Value = 2030 ± 330 mg/kg
                                     F requency




                                                  6
                                                  4
                      400 0                                                                                         Uncertainties
                                                  2
                                                  0
                                                                                                                    reported by
                      350 0                           <-3   -3-2   -2-1   -1-0    0-1        1-2    2-3   >3        participants.
                                                             T arget SD from Assigned Value
                      300 0
    Results (mg/kg)




                      250 0


                      200 0


                      150 0


                      100 0


                       50 0


                         0
                              12     8                5      7      21       11         16         19     4    13   20    3    17     9    10   15   1    18    6    Md   R.A.   H.V.   S

                                                                                                                     Laboratory


                                                                          Figure 1 Guide to Presentation of Results
4.2                     Assigned Value
The assigned value is defined1 as: ‘value attributed to a particular property of a proficiency
test item.’ In this study property is the mass fraction of analyte. Assigned values were the
robust average of participants’ results; the expanded uncertainties were estimated from the
associated robust standard deviations.
4.3                     Between-Laboratory Coefficient of Variation
The between laboratory coefficient of variation is a measure of the between laboratory
variation that in the judgement of the study coordinator would be expected from participants
given the analyte concentration. It is important to note this is not the coefficient of variation of
participant results.
4.4                     Target Standard Deviation
The target standard deviation (σ) is the product of the assigned value () and the between-
laboratory coefficient of variation (CV). This value is used for calculation of participant
z-score.
                        σ =  * CV                                                       Equation 1




8                                                                                            AQA 10-11 Hydrocarbons in Soil
4.5       z-Score
For each participant result a z-score is calculated according to Equation 2 below:
            (  X )
      z                          Equation 2
               
where:
      z      is z-score
            is participant result
            is the study assigned value
            is the target standard deviation from equation 1
A z-score with absolute value (|z|):
    |z|  2 is satisfactory;
    2 < |z|  3 is questionable;
    |z| > 3 is unsatisfactory.
4.6   En-Score
The En-score is complementary to the z-score in assessment of laboratory performance.
En-score includes measurement uncertainty and is calculated according to Equation 3 below:
               (  X )
      En                         Equation 3
               U U X
                2    2



where:
      En     is En-score
            is a participant’s result
            is the assigned value
      U     is the expanded uncertainty of the participant’s result
      UX     is the expanded uncertainty of the assigned value
An En-score with absolute value (|En|):
    |En|  1 is satisfactory;
    |En| > 1 is unsatisfactory.
4.7   Traceability and Measurement Uncertainty
Laboratories accredited to ISO/IEC Standard 17025:20058 must establish and demonstrate the
traceability and measurement uncertainty associated with their test results.
Guidelines for quantifying uncertainty in analytical measurement are described in the
Eurachem /CITAC Guide.9
4.8   Robust Average
The robust averages and associated expanded measurement uncertainties were calculated
using the procedure described in ‘ISO13528:2005(E), Statistical methods for use in
proficiency testing by interlaboratory comparisons’.10




                                   AQA 10-11 Hydrocarbons in Soil                            9
5      TABLES AND FIGURES
                                                 Table 5
Sample Details
Sample No.            S1
Matrix.               Soil
Analyte.              TPH
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty       z-Score     En-Score
1                      2540                380                  1.67        1.01
3                      2191                438                  0.53        0.29
4                      2131                307                  0.33        0.22
5                      1019                 89                 -3.32       -2.96
6                      6299                NR                 14.02       12.94
7                      1300                180                 -2.40       -1.94
8                       959                260                 -3.52       -2.55
9                      2265.25             NR                   0.77        0.71
10                     2356                573                  1.07        0.49
11                     1650                100                 -1.25       -1.10
12                      805                NR                  -4.02       -3.71
13                     2160                NR                   0.43        0.39
15                     2500                750                  1.54        0.57
16                     1800                NR                  -0.76       -0.70
17                     2209                NR                   0.59        0.54
18                     2900                580                  2.86        1.30
19                     1961                392                 -0.23       -0.13
20                     2160                NR                   0.43        0.39
21                     1450                NR                  -1.90       -1.76


Statistics
Assigned Value         2030           330
Spike                  2860           140
Homogeneity            2850           570
Results
Robust Average         2030           330
Median                 2160           260
Mean                   2140
N                        19
Max.                   6299
Min.                    805
Robust SD               570
Robust CV                28%




10                                    AQA 10-11 Hydrocarbons in Soil
                                                    8
                                                                Distr ibution of Results                                                                           Results: S1 - TPH
                                                                                                                                                                          Assigned Value = 2030 ± 330 mg/kg




                                       F requency
                                                    6
                                                    4
                     400 0
                                                    2
                                                    0
                     350 0                              <-3     -3-2        -2-1   -1-0         0-1          1-2     2-3    >3
                                                                 Target SD from Assigned Value
                     300 0
   Results (mg/kg)




                     250 0


                     200 0


                     150 0


                     100 0


                      50 0


                          0
                                 12    8                5        7            21           11          16           19      4           13          20         3   17       9          10          15           1    18    6      Md         R.A.         H.V.       S

                                                                                                                                                    Laboratory


                                                                                                                           z-Scores: S1 - TPH
                          Target Standard Deviation 305 mg/kg (Equivalent to 15% CV)
                     4
                                                                                                                                                                                                                                                    2.9
                     3

                     2                                                                                                                                                                                                     1.5     1 .7

                                                                                                                                                                                                                    1.1
                                                                                                                                                                                                        0 .8
                     1                                                                                                                                   0.4       0 .4
                                                                                                                                                                            0.5             0.6
                                                                                                                                             0 .3
z-Score




                     0
                                                                                                                             -0 .2

                     -1                                                                                             -0.8

                                                                                                  -1 .2
                     -2                                                            -1 .9

                                                                     -2.4
                     -3
                                                        -3 .3
                                      -3.5
                     -4
                              12       8                 5             7           21             11                16       19              4       13    20                3              17          9           10     15      1                18           6
                                                                                                                                                 Laboratory


                                                                                                                           En-Scores: S1 - TPH
                      4

                      3

                      2
                                                                                                                                                                                                                                                     1.3
                                                                                                                                                                                                                                       1.0
                      1                                                                                                                                                                      0.5
                                                                                                                                                                                                         0 .7
                                                                                                                                                                                                                     0.5    0.6
                                                                                                                                                         0 .4       0.4
En-Score




                                                                                                                                              0.2                               0 .3

                      0
                                                                                                                                - 0.1

                     -1                                                                                             -0.7
                                                                                                      -1.1

                     -2                                                            -1 .8
                                                                       -1.9

                                      -2.5
                     -3                                 -3 .0


                     -4       -3 .7

                              12       8                    5          7           21                 11            16          19             4         13        20           3           17            9         10     15          1            18           6
                                                                                                                                                    Laboratory


                                                                                                                                         Figure 2

                                                                                                                   AQA 10-11 Hydrocarbons in Soil                                                                                                                        11
                                                 Table 6
Sample Details
Sample No.            S1
Matrix.               Soil
Analyte.              C15-C28
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty
1                      2000                300
4                      1488                148
5                       760                 63
6                      5592                100
8                       710                191
9                      1698.50             679.4
10                     1860                452
11                     1270                 85
12                      604                NR
13                     1600                377
15                     1800                540
16                     1300                440
17                     1680                170
18                     2500                500
19                     1664                333
21                      890                NR


Statistics
Assigned Value        Not Set
Spike
Homogeneity
Results
Robust Average         1540           360
Median                 1630           270
Mean                   1713
N                        16
Max.                   5592
Min.                    604
Robust SD               514
Robust CV                32%




12                                    AQA 10-11 Hydrocarbons in Soil
                  600 0                               Results: S1 - C15-C28


                  500 0
Results (mg/kg)




                  400 0



                  300 0



                  200 0



                  100 0



                     0
                          12   8   5   21   11   16      4    13    19    17    9   15   10   1   18   6   Md   R.A.

                                                                   Laboratory

                                                               Figure 3




                                                  AQA 10-11 Hydrocarbons in Soil                                       13
                                                 Table 7
Sample Details
Sample No.            S1
Matrix.               Soil
Analyte.              C10-C14
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty
1                       290                 44
3                       455                 91
4                       444                 61
5                       160                 14
6                       707                 20
8                       249                 69
9                       328.64              95.46
10                      317                 77
11                      350                 12
12                       95.4              NR
13                      320                 58
15                      270                 80
16                      470                150
17                      384                 40
18                      380                 76
19                      297                 59
20                      260                140
21                      350                NR


Statistics
Assigned Value        Not Set
Spike                 Not Spiked
Homogeneity
Results
Robust Average          333            56
Median                  324            42
Mean                    340
N                        18
Max.                    707
Min.                     95.4
Robust SD                86
Robust CV                26%




14                                    AQA 10-11 Hydrocarbons in Soil
                  800
                                                        Results: S1 - C10-C14
                  700


                  600
Results (mg/kg)




                  500


                  400


                  300


                  200


                  100


                    0
                        12   5   8   20   15   1   19      10   13    9     11    21   18   17   4   3   16   6   Md   R.A.

                                                                     Laboratory

                                                                 Figure 4




                                                   AQA 10-11 Hydrocarbons in Soil                                             15
                                                 Table 8
Sample Details
Sample No.            S1
Matrix.               Soil
Analyte.              C29-C36
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty
1                       250                 38
4                       164                 74
5                        87                  8
9                       238.11              95.24
10                      179                 43
11                       29                  4
12                       43.6              NR
13                      240                 27
15                      370                110
16                      <50                NR
17                      145                 15
18                     <500                NR
19                     <100                 20
21                      210                NR


Statistics
Assigned Value        Not Set
Spike
Homogeneity
Results
Robust Average          174            75
Median                  179            61
Mean                    178
N                        11
Max.                    370
Min.                     29
Robust SD                90
Robust CV                50%




16                                    AQA 10-11 Hydrocarbons in Soil
                  600


                                               Results: S1 - C29-C36
                  500
Results (mg/kg)




                  400



                  300



                  200



                  100



                    0
                        11   12   5   17   4     10    21       9      13   1   15   19   16   18   Md   R.A.

                                                               Laboratory

                                                            Figure 5




                                               AQA 10-11 Hydrocarbons in Soil                                   17
                                                 Table 9
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              Total BTEX
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty       z-Score     En-Score
1                       690                100                  4.93        3.27
3                       244.36              48.9               -0.84       -0.84
4                       358.93              72                  0.65        0.53
5                       120.6               25.2               -2.44       -2.90
6                       424                 20                  1.49        1.82
7                       NR                 NR
8                       348                 97.56               0.50        0.34
9                       255.84             NR                  -0.69       -0.89
10                      293                 68                 -0.21       -0.18
11                      310                 12                  0.01        0.02
12                        5.3              NR                  -3.93       -5.06
13                      370                 71                  0.79        0.66
15                      450                130                  1.83        0.98
16                      190                NR                  -1.54       -1.98
17                      394                 40                  1.10        1.18
18                      300                 73                 -0.12       -0.10
19                      245                 49                 -0.83       -0.83
20                      303                 21                 -0.08       -0.09
21                      NR                 NR


Statistics
Assigned Value          309            60
Spike                 Not Spiked
Homogeneity             327            66
Results
Robust Average          309            60
Median                  303            45
Mean                    312
N                        17
Max.                    690
Min.                      5.3
Robust SD                99
Robust CV                32%




18                                    AQA 10-11 Hydrocarbons in Soil
                                                   8
                                                                Distr ibution of Results                                                          Results: S2 - Total BTEX
                                                                                                                                                              Assigned Value = 309 ± 60 mg/kg




                                      F requency
                                                   6

                     800                           4
                                                   2
                                                   0
                     700
                                                       <-3      -3-2       -2-1    -1-0     0-1      1-2       2-3    >3
                                                                    Target SD from Assigned Value
                     600
   Results (mg/kg)




                     500


                     400


                     300


                     200


                     100


                          0
                                12       5             16              3           19            9         10         18     20       11           8          4       13    17    6      15         1          Md     R .A.   H.V.

                                                                                                                                     Laboratory


                                                                                                               z-Scores: S2 - Total BTEX
                          Target Standard Deviation 77 mg/kg (Equivalent to 25% CV)
                     4

                     3
                                                                                                                                                                                                                    1.8
                     2                                                                                                                                                                                  1.5
                                                                                                                                                                                          1.1
                                                                                                                                                                                  0 .8
                     1                                                                                                                                            0.5
                                                                                                                                                                           0 .6
z-Score




                                                                                                                                                       0.0
                     0
                                                                                                                     -0 .2   -0.1          -0.1

                     -1                                                    -0.8           -0.8
                                                                                                      -0 .7


                                                         -1.5
                     -2
                                      -2 .4
                     -3

                     -4       -3 .9
                              12           5             16                 3             19           9             10      18         20     11                 8        4      13      17            6           15        1
                                                                                                                                    Laboratory


                                                                                                           En-Scores: S2 - Total BTEX
                      4
                                                                                                                                                                                                                              3.3

                      3
                                                                                                                                                                                                         1.8
                      2
                                                                                                                                                                                              1.2
                                                                                                                                                                                                                     1.0
                      1                                                                                                                                                     0.5    0.7
En-Score




                                                                                                                                                                  0 .3
                                                                                                                                                       0 .0
                      0
                                                                                                                      -0.2    -0.1         -0 .1

                     -1                                                     -0.8          -0.8         -0.9


                     -2
                                                             -2.0


                     -3                  -2 .9


                     -4
                              12              5              16             3             19               9         10       18           20          11          8         4    13          17         6          15        1
                                                                                                                                     Laboratory


                                                                                                                             Figure 6

                                                                                                           AQA 10-11 Hydrocarbons in Soil                                                                                            19
                                                Table 10
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              Xylenes
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty       z-Score     En-Score
1                       271                 41                  1.96        1.81
3                       142.46              28.5               -0.87       -1.01
4                       224                 45                  0.92        0.80
5                        76                 16                 -2.33       -3.38
6                       304                 20                  2.68        3.63
7                       NR                 NR
8                       197.75              55.87               0.35        0.25
9                       169.25              67.7               -0.28       -0.17
10                      179                 40                 -0.07       -0.06
11                      170                 10                 -0.26       -0.42
12                        3.1              NR                  -3.93       -6.63
13                      201                 28                  0.42        0.49
15                      230                 70                  1.05        0.64
16                      NR                 NR
17                      203                 20                  0.46        0.62
18                      160                 47                 -0.48       -0.41
19                      150                 30                 -0.70       -0.79
20                      175                 12                 -0.15       -0.24
21                       Nr                NR


Statistics
Assigned Value          182            27
Spike
Homogeneity             190            38
Results
Robust Average          182            27
Median                  177            21
Mean                    178.5
N                        16
Max.                    304
Min.                      3.1
Robust SD                44
Robust CV                24%




20                                    AQA 10-11 Hydrocarbons in Soil
                                                   8
                                                                Distr ibution of Results                                                          Results: S2 - Xylenes
                                                                                                                                                         Assigned Value = 182 ± 27 mg/kg




                                      F requency
                                                   6
                                                   4
                     350                           2
                                                   0
                                                       <-3      -3-2       -2-1      -1-0   0-1     1-2     2-3      >3
                     300
                                                                     Target SD from Assigned Value

                     250
   Results (mg/kg)




                     200


                     150



                     100



                      50



                          0
                               12        5              3             19          18          9           11         20          10          8    13     17         4          15         1    6     16         Md         R .A.     H.V.

                                                                                                                                      Laboratory


                                                                                                                   z-Scores: S2 - Xylenes
                          Target Standard Deviation 46 mg/kg (Equivalent to 25% CV)
                     4

                     3                                                                                                                                                                                                             2 .7


                                                                                                                                                                                                                     2.0
                     2
                                                                                                                                                                                              0.9     1.1
                     1                                                                                                                                                  0.4         0.5
                                                                                                                                                          0 .3
z-Score




                     0
                                                                                                                                      -0.2       -0 .1
                                                                                                           -0.3           -0.3
                                                                                            -0.5
                     -1                                      -0 .9
                                                                              -0.7



                     -2
                                           -2 .3
                     -3

                     -4       -3 .9
                              12                   5          3               19            18             9              11          20     10           8             13          17        4       15             1             6
                                                                                                                                      Laboratory


                                                                                                               En-Scores: S2 - Xylenes
                      4                                                                                                                                                                                                             3.6


                      3
                                                                                                                                                                                                                      1.8
                      2
                                                                                                                                                                                               0.8
                      1                                                                                                                                                  0.5
                                                                                                                                                                                     0.6                  0.6
En-Score




                                                                                                                                                              0.3

                      0
                                                                                                                                                  -0.1
                                                                                                           -0.2                       -0.2
                                                                                             -0.4                         -0.4
                     -1                                                       -0 .8
                                                             -1 .0

                     -2

                     -3
                                              -3 .4
                     -4
                              12                   5           3              19             18                9          11          20          10          8         13          17         4          15          1              6
                                                                                                                                      Laboratory


                                                                                                                                 Figure 7

                                                                                                          AQA 10-11 Hydrocarbons in Soil                                                                                                    21
                                                Table 11
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              Ethylbenzene
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty       z-Score     En-Score
1                        37                  6                  1.23        1.18
3                        23.14               3.5               -0.73       -0.93
4                        31.50               6.30               0.45        0.42
5                         9.4                2                 -2.67       -3.99
6                        42                 10                  1.94        1.26
7                       NR                 NR
8                        29.6                8.29               0.18        0.14
9                        25.44              10.18              -0.40       -0.26
10                       25.2                6.0               -0.44       -0.42
11                       28                  2.5               -0.04       -0.06
12                        0.7              NR                  -3.90       -6.42
13                       32                  4                  0.52        0.63
15                       37                 11                  1.23        0.74
17                       35.7               36                  1.05        0.20
18                       26                  6.8               -0.33       -0.29
19                       25                  5                 -0.47       -0.50
20                       26                  1.8               -0.33       -0.49
21                       Nr                NR


Statistics
Assigned Value           28.3            4.3
Spike
Homogeneity              36.0            7.2
Results
Robust Average           28.3            4.3
Median                   27.0            3.3
Mean                     27.1
N                        16
Max.                     42
Min.                      0.7
Robust SD                 6.9
Robust CV                24.4%




22                                    AQA 10-11 Hydrocarbons in Soil
                                                     8
                                                                       Distr ibution of Results                                                           Results: S2 - Ethylbenzene
                                                                                                                                                                         Assigned Value = 28.3 ± 4.3 mg/kg




                                     Frequency
                                                     6
                                                     4
                                                     2
                     50                              0
                                                             <-3       -3-2    -2 -1     -1-0       0-1          1-2    2-3     >3
                                                                          Target SD from Assigned Value

                     40
   Results (mg/kg)




                     30



                     20




                     10




                      0
                             12                  5                 3           19              10            9           18          20       11          8          4           13    17    1      15         6          Md         R.A.    H. V.

                                                                                                                                                   Laboratory


                                                                                                                       z-Scores: S2 - Ethylbenzene
                          Target Standard Deviation 7.1 mg/kg (Equivalent to 25% CV)
                     4

                     3
                                                                                                                                                                                                                                            1 .9
                     2
                                                                                                                                                                                                                   1.2         1.2
                                                                                                                                                                                                     1.0
                     1                                                                                                                                                                0.5    0.5
z-Score




                                                                                                                                                                          0 .2

                     0
                                                                                                                                                              0 .0
                                                                                                      -0.4              -0.4         -0.3          -0.3
                                                                                       -0.5
                     -1                                                -0 .7



                     -2

                     -3                          -2 .7



                     -4      -3 .9
                             12                      5                  3              19             10                 9           18        20     11                   8          4      13      17            1           15           6
                                                                                                                                               Laboratory


                                                                                                                       En-Scores: S2 - Ethylbenzene
                      4

                      3

                      2
                                                                                                                                                                                                                    1.2                      1.3

                      1                                                                                                                                                                0.4
                                                                                                                                                                                              0.6                               0.7
En-Score




                                                                                                                                                                           0.1                           0.2

                      0
                                                                                                                                                              -0.1
                                                                                                                         -0.3         -0.3
                                                                                       -0 .5              -0.4                                     -0.5
                     -1                                                -0 .9


                     -2

                     -3

                     -4
                                                     -4 .0
                             12                          5               3             19                 10              9           18           20         11           8           4     13          17         1          15             6
                                                                                                                                               Laboratory


                                                                                                                                             Figure 8

                                                                                                                       AQA 10-11 Hydrocarbons in Soil                                                                                                23
                                                Table 12
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              Toluene
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty       z-Score     En-Score
1                       160                 24                  2.67        1.77
3                        76.42              11.5               -0.82       -0.67
4                       100                 26                  0.17        0.11
5                        34                  7                 -2.58       -2.22
6                        77                 10                 -0.79       -0.66
7                       NR                 NR
8                       106                 29.7                0.42        0.25
9                        60.35              24.14              -1.49       -0.98
10                       87.1               20                 -0.37       -0.26
11                      110                  1.7                0.58        0.52
12                        1.4              NR                  -3.94       -3.50
13                      130                 15                  1.42        1.10
15                      170                 51                  3.08        1.28
16                       63                 17                 -1.38       -1.03
17                      151                 15                  2.29        1.78
18                      110                 18                  0.58        0.43
19                       69                 14                 -1.12       -0.89
20                       98                  8.0                0.08        0.07
21                      NR                 NR


Statistics
Assigned Value            96           27
Spike                 Not Spiked
Homogeneity               95           20
Results
Robust Average           96            27
Median                   98            22
Mean                     94.3
N                        17
Max.                    170
Min.                      1.4
Robust SD                45
Robust CV                47%




24                                    AQA 10-11 Hydrocarbons in Soil
                                                   6
                                                                  Distribution of Results                                                                Results: S2 - Toluene
                                                                                                                                                                    Assigned Value = 96 ± 27 mg/kg




                                      F requency
                                                   4

                                                   2
                     180
                                                   0
                     160                               <-3        -3-2    -2-1       -1 -0     0-1      1-2           2-3   >3
                                                                    Target SD from Assigned Value
                     140
   Results (mg/kg)




                     120


                     100

                      80

                      60

                      40


                      20

                          0
                                12          5            9               16          19             3             6          10     20        4          8          11       18    13    17     1          15          Md       R .A.    H.V.

                                                                                                                                            Laboratory


                                                                                                                        z-Scores: S2 - Toluene
                          Target Standard Deviation 24 mg/kg (Equivalent to 25% CV)
                     4
                                                                                                                                                                                                                                        3 .1
                     3                                                                                                                                                                                                      2.7
                                                                                                                                                                                                                2.3

                     2                                                                                                                                                                              1.4


                     1                                                                                                                                                   0.4
                                                                                                                                                                                  0 .6   0 .6
z-Score




                                                                                                                                                  0.1        0.2

                     0
                                                                                                                                    -0.4
                     -1                                                                                   -0 .8             -0 .8
                                                                                             -1.1
                                                                              -1.4
                                                             -1.5
                     -2

                                         -2 .6
                     -3

                     -4       -3 .9
                              12              5               9               16             19               3              6      10         20     4                  8        11     18     13              17          1           15
                                                                                                                                           Laboratory


                                                                                                                       En-Scores: S2 - Toluene
                      4

                      3

                                                                                                                                                                                                                 1.8         1.8
                      2
                                                                                                                                                                                                                                         1.3
                                                                                                                                                                                                     1.1
                      1                                                                                                                                                            0.5    0.4
En-Score




                                                                                                                                                                         0 .2
                                                                                                                                                  0 .1       0 .1

                      0
                                                                                                                                     -0.3
                     -1                                                                      -0.9
                                                                                                              -0.7           -0.7
                                                             -1.0             -1.0

                     -2
                                            -2 .2

                     -3
                              -3 .5
                     -4
                              12                   5          9               16             19               3               6      10           20          4           8       11     18         13          17           1           15
                                                                                                                                            Laboratory


                                                                                                                                    Figure 9

                                                                                                              AQA 10-11 Hydrocarbons in Soil                                                                                                    25
                                                Table 13
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              Benzene
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty
1                         4.5                0.7
3                         2.34               0.35
4                         3.43               0.07
5                         1.2                0.2
6                         0                 10
7                       NR                 NR
8                        14.8                3.7
9                         0.80               0.32
10                        1.43               0.33
11                        3.4                0.3
12                        0.1              NR
13                        5.2                1.0
15                        6.2                1.9
16                        2.2                0.45
17                        4.85               1.00
18                        5.0                1.4
19                        1.17               0.23
20                        3.5                0.21
21                      NR                 NR


Statistics
Assigned Value        Not Set
Spike
Homogeneity               4.9            1.0
Results
Robust Average            3.1            1.4
Median                    3.4            1.4
Mean                      3.5
N                        17
Max.                     14.8
Min.                      0
Robust SD                 2.4
Robust CV                77%




26                                    AQA 10-11 Hydrocarbons in Soil
                                                       Results: S2 - Benzene
                  10

                   9

                   8

                   7
Results (mg/kg)




                   6

                   5

                   4

                   3

                   2

                   1

                   0
                       6   12   9   19   5   10   16      3    11    4     20    1   17   18   13   15   8   Md   R.A.   H.V.

                                                                    Laboratory

                                                               Figure 10




                                                  AQA 10-11 Hydrocarbons in Soil                                                27
                                                Table 14
Sample Details
Sample No.            S2
Matrix.               Soil
Analyte.              C6-C9
Units                 mg/kg


Participant Results
Lab Code              Concentration      Uncertainty
1                       490                 74
3                        NT                 NT
4                       878                176
5                        NT                 NT
6                       150                 20
8                       522                 78.3
9                       470.91             188.36
10                      NR                 NR
11                      510                 70
13                      410                 83
15                     1300                380
16                      210                 55
17                      539                 55
18                      560                170
19                      349                 70


Statistics
Assigned Value        Not Set
Spike
Homogeneity
Results
Robust Average          488            95
Median                  532            71
Mean                    532.4
N                        12
Max.                   1300
Min.                    150
Robust SD               111
Robust CV                22%




28                                    AQA 10-11 Hydrocarbons in Soil
                  180 0
                                             Results: S2 - C6-C9
                  160 0


                  140 0
Results (mg/kg)




                  120 0


                  100 0


                   80 0


                   60 0


                   40 0


                   20 0


                     0
                          6   16   19   13       9     1     11      8       17       18   4   15   10   3   5   Md   R.A.

                                                                         Laboratory

                                                                   Figure 11




                                                      AQA 10-11 Hydrocarbons in Soil                                         29
           10



            8



            6



            4



            2
 z-Score




            0
                                                                                                            1

            -2



            -4



            -6



            -8



           -10   1       4   5            6   7   8   9                   12    13           16                                              21                All
                     3                                    10 11                      15                17       18   19   20
                                                                               Lab code

                                                      Figure 12 Summary of z-scores by laboratory
           10


            8


            6


            4


            2
 z-Score




            0


            -2


            -4


            -6


            -8
                                                                                                                           S2-Ethylbenzene
                                                          S2-Total BTEX
                                                          S2-Total BTEX




           -10
                                                                                                                                                  S2-Toluene
                                                                                          S2-Xylenes
                                 S1-TPH
                                 S1-TPH




                                                                                                        Analyte


                                                      Figure 13 Summary of z-Scores by Analyte




30                                                                        AQA 10-11 Hydrocarbons in Soil
           10



            8



            6



            4



            2
En-Score




            0

                                                                                    1

            -2



            -4



            -6



            -8



           -10   1   3   4   5   6   7   8    9   10 11   12    13   15   16   17       18   19   20   21   All
                                                               Lab code

                                             Figure 14 Summary of En-scores by laboratory.




                                                          AQA 10-11 Hydrocarbons in Soil                          31
6     DISCUSSION OF RESULTS
6.1   Assigned Value - Total Petroleum Hydrocarbons in Sample S1
The robust average of participants’ results was used as the assigned value for TPH in Sample
S1 and for toluene, xylenes, ethylbenzene and total BTEX in Sample S2. The robust averages
and associated expanded uncertainties were calculated using the procedure described in
‘ISO13528:2005(E), Statistical methods for use in proficiency testing by interlaboratory
comparisons’.10 Appendix 3 sets out the calculation for the expanded uncertainty of the robust
average of Toluene in Sample S2.
No assigned value was set for benzene in Sample S2 because there was no consensus amongst
participants.
Traceability: The consensus of participants’ results is not traceable to any external reference,
so although expressed in SI units, metrological traceability has not been established.
No assigned values were set for the hydrocarbon ranges. The study coordinator believe this
information is semi-quantitative and intended to help identify the nature of the hydrocarbon
pollution. The ranges used and the methods for deciding the boundaries of these ranges are
not standardised. Scoring in this situation would not be appropriate.
6.2   Measurement Uncertainty Reported by Participants
With the issue of ISO Standard 17025,8 there is a requirement for the estimation of
measurement uncertainty for chemical analysis results and for laboratories to report this
uncertainty in specific circumstances, including ‘when the client’s instruction so requires’.
Participants were asked to report an estimate of the expanded measurement uncertainty
associated with their results and the basis of this uncertainty estimate (Table 3). If no TPH
result was reported, then TPH was calculated by the study coordinator by summing the
individual hydrocarbon ranges and no estimate of the uncertainty of the TPH result was made.
Of 160 numeric results, 139 (87%) were reported with an associated expanded measurement
uncertainty. The magnitude of these uncertainties was within the range 1.5 – 101% relative,
115 were within what the study coordinator believes to be a reasonable range of 10 to 100 %
relative.
Some results and uncertainties were reported with more significant figures than appropriate.
Uncertainties should usually be reported with no more than two significant figures, and the
result expressed with the corresponding number of decimal places. For example, a result of
169.25 ± 67.7 mg/kg for xylenes may be better reported as 169 ± 68 mg/kg; see Ref 9, Section
9.5.1.
6.3   z-Score
Based on practical experience and published models11 the expected between-laboratory
coefficient of variation (CV) should be approximately 15% – 25% for the concentrations of
hydrocarbons in the study samples. A target standard deviation equivalent to 15% CV was
used to calculate z-scores for TPH in Sample S1; a target standard deviation equivalent to
25% CV was used to calculate z-scores for BTEX components in Sample S2.
Of 85 z-scores, 66 (78%) returned a satisfactory score of |z|  2.
The dispersal of participants’ z-scores is graphically presented in Figures 12 and 13.
6.4   En-Score
Where a laboratory did not report an expanded uncertainty with a result, an expanded
uncertainty of zero (0) was used to calculate the En-score.

32                                AQA 10-11 Hydrocarbons in Soil
Of 85 En-scores, 54 (64%) returned a satisfactory score of |En|  1.
The dispersal of participants’ En-scores is graphically presented in Figure 14.
6.5              Participants’ Analytical Methods
For TPH in Sample S1, participants used solvent extraction using dichloromethane, acetone or
alkane solvents, either alone or in various mixtures. Sonication, solvent extraction, and
Accelerated Solvent Extraction (ASE) techniques were used. Three participants reported
using a silica cleanup and two used Florisil. Sixteen participants used GC with FID, four used
GC/MS. No trends in the reported results were evident with either the extraction technique or
the detector used (Figures 15 and 16).
For BTEX in Sample S2, most participants used a solvent extraction followed by purge-and-
trap/GC/MS. Methanol was the most commonly used solvent, acetone and dichloromethane
were also used in various mixtures. Two laboratories used purge-and-trap with GC/FID.
Three laboratories used headspace analysis with either GC/MS or GC/FID. Given this variety
of methods, no attempt to correlate results with methods was made.

                4000                                    offscale 6299



                3000
  TPH (mg/kg)




                2000



                1000



                   0
                       0          1                 2                         3       4               5
                                                        Extraction Solvent


1 = acetone/dichloromethane 2 = dichloromethane 3 = acetone/hexane or heptane
4 = acetone/dichloromethane/hexane 5 = solvent not specified.
                             Figure 15 Sample S1 TPH results vs extraction solvent.

                4000                                                                  offscale 6299



                3000
  TPH (mg/kg)




                2000



                1000



                  0
                       0                            1                             2
                                                    GC/FID (1) or GC/MS (2)



                            Figure 16 Sample S1 TPH results vs detection technique.


                                          AQA 10-11 Hydrocarbons in Soil                              33
6.6                    Certified Reference Materials (CRM)
Participants were requested to indicate on the result sheet whether matrix reference materials
had been used as part of the quality assurance for the analysis.
Two participants reported using matrix reference materials as follows:
Laboratory 12: Commercial petrol and diesel.
Laboratory 19: natural matrix certified reference material obtained from Resource
Technology Corporation.
Eight laboratories reported using certified reference standards.
6.7                    Comparison with Previous Proficiency Tests.
The proportions of satisfactory, questionable and unsatisfactory z-scores were similar over the
past three NMI PTs (Figure 17).

                                                      Summary of Performance: TPH in Soil

                      120%                                                                                 n = total number of scores.
                                   n = 40                          n = 16                       n = 19
                      100%
                                                                    6%
                                   15%
                                                                   13%                           21%
  % of Total Scores




                      80%          10%
                                                                                                 11%
                                                                                                                      Unsatisfacory
                      60%
                                                                                                                      Questionable
                                                                                                                      Satisfactory
                      40%                                          81%
                                   75%
                                                                                                 68%

                      20%


                       0%
                                 AQA 09-06                       AQA 09-15                     AQA 10-11
                                                                   Study



                                                      Summary of Performance: BTEX in Soil
                                             n = 58                                  n = 66
                      100%                                                                                 n = total number of scores.
                                                                                          9%
                                             14%
                      90%
                                                                                      11%
                      80%                    14%

                      70%
  % of Total Scores




                      60%
                                                                                                                      Unsatisfacory
                      50%
                                                                                                                      Questionable
                      40%                                                             80%                             Satisfactory
                                             72%
                      30%

                      20%

                      10%

                       0%
                                         AQA 09-15                                  AQA 10-11
                                                                   Study


BTEX was not measured in AQA 09-06.
                              Figure 17 Performance in the past three Hydrocarbon in Soil PTs.


34                                                       AQA 10-11 Hydrocarbons in Soil
7    REFERENCES
     [1] ISO/IEC 17043:2010, Conformity assessment – General requirements for
    proficiency testing, (2010), ISO, Geneva.
    [2] NMI Chemical Proficiency Testing Study Protocol.
    http://www.measurement.gov.au → services → chemical proficiency testing
     [3] NMI Chemical Proficiency Testing Statistical Manual.
    http://www.measurement.gov.au → services → chemical proficiency testing
     [4] ILAC-G13:2007, Guidelines for the requirements for the competence of providers of
    proficiency testing schemes, (2007), ILAC.
     [5] Thompson, M. Ellison S. L. R and Wood, R., (2006), The international harmonized
    protocol for proficiency testing of (chemical) analytical laboratories, Pure Appl. Chem. 78,
    145-196.
     [6] National Environmental Protection Council Schedule B(1) Guidelines on the
    Investigation Levels for Soil and Groundwater
    http://www.ephc.gov.au/sites/default/files/ASC_NEPMsch__01_Investigation_Levels_199
    912.pdf (Accessed November 2010).
     [7] Worrall, R.D., “Total Petroleum Hydrocarbons in Soil: Storage Stability Study”,
    (1996), ACSL Public Interest Project, AGAL, Canberra, Australia.
     [8] ISO/IEC 17025:2005 General requirements for the competence of testing and
    calibration laboratories (2005) ISO, Geneva, Switzerland.
     [9] Eurachem/CITAC Guide Quantifying uncertainty in analytical measurement second
    edition, (2000), http://www.eurachem.org/guides/pdf/QUAM2000-1.pdf (Accessed
    November 2010).
     [10] ISO13528:2005(E), Statistical methods for use in proficiency testing by
    interlaboratory comparisons. (2005) ISO, Geneva, Switzerland.
     [11] Horwitz, W., (1982), Evaluation of analytical methods used for regulation of food
    and drugs, Anal. Chem., 54, 67A-76A.




                                  AQA 10-11 Hydrocarbons in Soil                              35
APPENDIX 1. PARTICIPANT LABORATORIES


Advanced Analytical Australia, NSW.                      ALS Water Resources Group,VIC.
AMAL Analytical, VIC.                                    Analytical Reference Laboratory (WA) Pty Ltd, WA.
AsureQuality Limited Wellington Laboratory,
                                                         ChemCentre, WA.
NEW ZEALAND
                                                         Department of Environment and Climate Change
CSIRO CELS Floreat                                       (NSW), Environmental, Forensic and Analytical
                                                         Science Section. NSW
Flinders Analytical, Faculty of Science & Engineering,   M & L Laboratory Services Pty Ltd. SOUTH
Flinders University, SA.                                 AFRICA.
MGT Environmental Consulting Pty Ltd, VIC                MPL Laboratories (Envirolab Services WA)
Nabbir Laboratory Sdn Bhd, MALAYSIA                      National Measurement Institute, WA.
Queensland Health, Forensic and Scientific Services,
                                                         SGS - Coburg, VIC.
QLD.
SGS Environmental Services, NSW.                         SGS Environmental Services Newburn, WA.
Simmonds and Bristow Pty Ltd, QLD                        Tweed Shire Council Tweed Laboratory Centre, NSW.
Water Care Services Limited Laboratory Services,
NEW ZEALAND.




36                                    AQA 10-11 Hydrocarbons in Soil
APPENDIX 2 - SAMPLE PREPARATION AND HOMOGENEITY TESTING
A2.1 Diesel Fuel Preparation
Diesel fuel was purchased from a local retail outlet and treated to remove volatiles.
Approximately 500 mL of diesel fuel was placed in a heated (80C) open container and
sparged with nitrogen. Treatment continued until the GC-FID chromatogram indicated that
essentially all the hydrocarbons eluting before C10 had been removed.
A2.2 Test sample Preparation
Test samples for this study were prepared at the National Measurement Institute,
Pymble, NSW.
The matrix material was prepared as follows:
    Soil was collected from the grounds of the National Measurement Institute at Pymble.
    The moist soil was placed in metal or Pyrex trays and dried at 120ºC for at least two
     hours.
    Dried soil was sieved and the fraction in the range 350-850 µm collected and mixed
     using a drum hoop mixer.
Sample S1 was prepared in the following manner:
    A 2.8 kg portion was accurately measured into a stainless steel pot for mixing.
     Sufficient dichloromethane was added with mixing to moisten.
    An accurately measured aliquot of sparged diesel was added to give the required
     concentration. The soil was stirred to mix the diesel with the soil and dichloromethane.
     The solvent was allowed to evaporate off until dryness.
    Using the Retsch PT 100 sample divider the dry soil was divided into ten 280 g
     portions. Five lots of two portions were then divided to yield ten 56 g portions which
     were then placed in glass jars. These jars were labelled in numeric fill order.
    The samples were then stored in a refrigerator.
Sample S2 was prepared in the following manner:
    A 10 litre clamp topped drum was weighed and 3 kg of dried sieved soil was placed in
     it. The drum was placed in the freezer over the weekend.
    On the day of spiking the diesel was weighed into a cooled beaker.
    The drum containing the soil was removed from the freezer and the lid removed.
    As quickly as possible the un-leaded petrol was added to the diesel in the beaker and
     the mass was determined. The diesel and un-leaded petrol were then added to the soil,
     sealed and vigorously shaken.
    The sealed drum was then packed into another large drum and surrounded by cold gel-
     packs. The drums were then tumbled for 90 minutes on a hoop mixer. The drum was
     checked for leakage and then tumbled for another three hours.
    After tumbling the soil was checked to ensure that there was no agglomeration of soil
     particles.
    The soil was then taken into a walk-in refrigerator with the glass jars which had also
     been kept in the freezer.
    As quickly as possible the soil was scooped into the glass jar, tapped, topped up to
     minimise the vapour space and sealed.
    The caps were sealed with Parafilm, the jars labelled and stored in a freezer.

                                AQA 10-11 Hydrocarbons in Soil                            37
Expanded uncertainties were estimated for the TPH spiked concentration. Contributions to
these uncertainties included the gravimetric and volumetric operation involved in spiking the
samples.
A2.3 Homogeneity Testing
Seven bottles were selected at random from each of Sample S1 and Sample S2. Sample S1
was analysed for TPH and S2 was analysed for BTEX. NMI hold third party (NATA)
accreditation to ISO 17025 for these tests.
The results of the homogeneity testing are presented in Tables 15-16.
                           Table 15 Homogeneity Testing S1 TPH


                           Jar Fill           TPH               TPH
                           Number            (mg/kg)           (mg/kg)
                              3               2745              2516
                             11               2531              3232
                             13               2579              3319
                             18               2533              3213
                             25               2743              3092
                             30               2614              3040
                             44               2698              3049
                        Mean                           2850
                        CV                             10%


                       Table 16 Homogeneity Testing S2 Total BTEX
                             Jar Fill         BTEX              BTEX
                             Number          (mg/kg)           (mg/kg)
                                8              315               329
                               13              268               306
                               23              349               316
                               26              293               293
                               30              376               336
                               31              321               364
                               45              337               368
                        Mean                            326
                        CV                             9.6%




38                                 AQA 10-11 Hydrocarbons in Soil
APPENDIX 3 - ROBUST AVERAGE AND ASSOCIATED UNCERTAINTY
The robust average was calculated using the procedure described in ‘ISO13258:2005(E),
Statistical methods for use in proficiency testing by interlaboratory comparisons – Annex C10
the uncertainty was estimated as:
       urob av = 1.25*Srob av / p                                    Equation 4
       where:
       urob av        robust average standard uncertainty
       Srob mean      robust average standard deviation
       p              number of results
The expanded uncertainty (Urob av) is the standard uncertainty multiplied by a coverage factor
of 2 at approximately 95% confidence level.
A worked example is set out below in Table 19.
               Table 17 Uncertainty of robust average for toluene in Sample S2
                               No. results (p)        17
                               Robust Average         95.8 mg/kg
                               Srob av                44.7 mg/kg
                               urob av                13.6 mg/kg
                               k                       2
                               Urob av                27.1 mg/kg


The assigned value for toluene in Sample S2 is 96  27 mg/kg.




                                    AQA 10-11 Hydrocarbons in Soil                          39
APPENDIX 4 - ACRONYMS AND ABBREVIATIONS


BTEX          Benzene, Toluene, Ethylbenzene, Xylenes
CRM           Certified Reference Material
CV            Coefficient of Variation
|En|          Absolute value of an En-score
GC/FID        Gas Chromatography Flame Ionization Detector
GC/MS         Gas Chromatography Mass spectrometry
ILAC          International Laboratory Accreditation Cooperation.
ISO           International Standards Association
Max           Maximum value in a set of results
Md            Median value in a set of results
Min           Minium value in a set of results
NATA          National Association of Testing Authorities
NEPC          National Environmental Protection Council
NMI           National Measurement Institute (of Australia)
NR            Not Reported
NT            Not Tested
PID           Photo Ionization Detector
PT            Proficiency Test
Robust CV     Robust Coefficient of Variation
Robust SD     Robust Standard Deviation
S             Spiked or formulated concentration of a PT sample
Target SD     Target standard deviation
TPH           Total Petroleum Hydrocarbons.
            Target standard deviation
|z|           Absolute value of a z-score




40                         AQA 10-11 Hydrocarbons in Soil

								
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