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Analysis of edible oils and fats

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					                                                                          No. 141/3 e


Application Bulletin
Of interest to:   Foodstuffs, Oil and Fat industry                                      A B E F 1, 7




                      Analysis of edible oils and fats

Summary
                  This Bulletin describes the following analytical methods, documented as far as
                  possible with actual experimental curves and instrument reports:
                  • Water content according to the Karl Fischer method
                  • Oxidation stability according to Rancimat method (AOCS Cd 12b-92)
                  • Iodine number
                  • Peroxide number
                  • Saponification number
                  • Acid number, degree of acidity and free fatty acids (FFA)
                  • Hydroxyl number
                  • Nickel traces, using polarography
                  In the use of these methods, special care was taken to avoid using chlorinated sol-
                  vents.




1. Determination of water content
                  The coulometric method is preferred for this analysis because of the low water
                  contents of pure oils and fats. For butter and margarines, which exhibit a relatively
                  high water content, the volumetric method should be employed.

Apparatus and accessories

                  • KF Coulometer, cell with diaphragm (for the coulometric method)
                  • Titrino or Titrando with magnetic swing-out stirrer and exchange unit and Dos-
                    ino or Dosimat (for the volumetric method)

Reagents
                  As mentioned above, for ecological reasons, only reagents free of pyridine and
                  halogenated hydrocarbon should be used, e.g.:
                  •   Hydranal Coulomat AG-H* (Coulometry)
                  •   Hydranal Composite 5*
                  • Solvent mixture: methanol / 1-decanol 2:1
                  * Hydranal = Riedel de Haen
                                      Application Bulletin                                No. 141/3 e
Analysis of edible oils and fats                                                                Page 2

Analysis
                Coulometric method for samples with low water content (edible oil / frying
                oil, hard fat)
                First, dry the cell (conditioning) until a constant drift is achieved (< 10 µg/min is
                typical), then fill a dry syringe (without needle) 3 times with the sample and discard
                it. Fill again, and add approx. 0.5 g to 1 g sample to the titration cell and titrate the
                water content. Hard fats will melt first.

                Volumetric method for samples with relatively high water content (butter,
                margarine)
                Add approx. 30 mL solvent mixture to the titration vessel and allow to dry (condi-
                tioning) up to a constant drift of approx. 10 ... 20 µL/min. Homogenise* the sample
                and fill it into a dry syringe (without needle). Add approx. 0.3 g sample to the titra-
                tion vessel and titrate.
                * In these samples, the distribution of water is inhomogeneous. It should not be
                heated over 25 oC, otherwise phase separation may occur.

Results

                  Olive oil            AVG(3) = 260.0       1.5 ppm
                  Peanut oil           AVG(3) = 253.7       1.1 ppm
                  Cooking butter       AVG(3) = 15.40       0.22 %
                  Margarine            AVG(3) = 18.87       0.13 %




2. Determination of the oxidation stability


Apparatus and accessories

                • Rancimat
                • Ev. GLP Test Set


Analysis
                Test first the temperature with the GLP Test Set according to the instructions for
                use and enter the temperature difference on the instrument. Weigh out 3 g sample
                into the reaction vessel (melting beforehand if necessary) taking care that none of
                the sample touches the sides of the vessel.
                Fill each adsorption vessel with 60 mL dist. H2O. The induction times are usually
                determined by 120 oC and 20 L/h air throughput. (See instructions for use of the
                Rancimat).
                                                         Application Bulletin                                                                     No. 141/3 e
Analysis of edible oils and fats                                                                                                                         Page 3

Results
                 (Induction times in h)
                  Samples                                               100 oC            110 oC            120 oC           130 oC
                  Olive oil                                              17.6               8.2               3.7              1.9
                  Olive oil extra virgin                                 53.1              22.8              10.2              4.3
                  Colza oil                                              18.4               9.2               5.2              2.5
                  Corn seed oil                                          20.2              9.3                5.0             2.4
                  Thistle oil                                             7.6               3.6               1.9              1.0
                  Sunflower oil                                          10.3               4.5               2.4              1.2
                  Peanut oil                                             15.4               6.4               4.0              1.7
                  Cooking butter                                         36.8              17.4               8.4              4.2
                  Margarine                                              35.6              19.9              12.4              6.7



Figures
                 Through a temperature increase of 10 oC, the induction times are reduced approx.
                 to the half!
                 The figures show a report of the Rancimat 743 for olive oil.

Curves:                                              Olivenoel /               Olivenoel /             Olivenoel /           olive oil /
                                                   Induction time
                                                   Stability time
                                64.1 µS/cm




                                     0.0                  2.5            5.0        7.5        10.0         12.5     15.0           17.5
                                                                                               h




Extrapolation:                               135                                                                                           2
                                                                                                                                           r = 0.9989
                                             130
                                                                                                                                           standard factor = 2.096
                                             125

                                                                                                                                           Shelf life for storing tem-
                                             120
                                                                                                                                           perature (calculated by the
                                             115
                                                                                                                                           instrument)
                                °C




                                                                                                                                           0°C = 3.2 years
                                             110                                                                                           4°C = 2.4 years

                                             105


                                             100


                                              95
                                                                2*100             4*100      6*100    8*100 101             2*101
                                                                                             h
                                      Application Bulletin                                  No. 141/3 e
Analysis of edible oils and fats                                                                  Page 4



3. Determination of the iodine number


Apparatus and accessories
                • Titrino or Titrando with Dosino or Dosimat
                • Magnetic swing-out stirrer
                • Exchange unit
                • Pt Titrode 6.0431.100 with electrode cable 6.2104.020


Reagents

                • Titrant: c(Na2S2O3) = 0.1 mol/L
                • Reaction solution: c(ICl) = 0.1 mol/L in glacial acetic acid
                • Catalyst solution: w(Mg acetate) = 3 % in glacial acetic acid
                • Glacial acetic acid: w(acetic acid) = 96 ... 98 %
                • Potassium iodide: w(KI) = 10 % in dist. H2O (stored in a dark bottle)


Analysis
                According to the expected iodine number, weigh 0.1 ... 1 g of the sample in an Er-
                lenmeyer flask and dissolve in 20 mL glacial acetic acid. While stirring, add
                25.0 mL reaction solution (ICl) and 10 mL catalyst. Close the flask and allow to
                stand for exactly 5 min in a dark place. Then add 15 mL KI solution, rinse quantita-
                tively with dist. H2O into a beaker and back-titrate the excess of iodine immediately
                with c(Na2S2O3) = 0.1 mol/L. Prepare a blank control without sample. Treat it ex-
                actly the same way and titrate. Store the blank consumption as the Common Vari-
                able C30 in the titrator. After each titration, rinse the electrode and the burette tip
                carefully with ethanol then dist. H2O, to completely remove the resulting sticky pre-
                cipitates.


Calculations
                Iodine number IN (g Iodine / 100 g) = (C30 - EP1) * C01 / C00

                C00 = sample weight in g
                C01 = 1.269 (equivalent weight of iodine)
                C30 = mL thiosulphate for the blank
                EP1 = mL thiosulphate for the sample

Remarks
                • Pay heed that a minimum of 25 mL thiosulphate solution is used for the back-
                  titration of the reaction solution. If this is not the case, there is a risk that the io-
                  dine numbers found will be too low (incomplete reaction). We have discovered
                  that with olive and sunflower oils the analysis must be carried out with a sample
                  weight of less than 0.4 g.
                                        Application Bulletin                               No. 141/3 e
Analysis of edible oils and fats                                                                 Page 5

                  • Contrary to most methods (e.g. Wijs), neither the poisonous CCI4 nor Hg-
                    acetate were used in this analysis. The obtained results corresponded well.
                  • The replacement of Hg-acetate with either Mg-acetate or Na-acetate was de-
                    scribed in the Japanese Patent No. 56-22967 (1981).


Results
                   Peanut oil            AVG(3) = 94.3
                   Sunflower oil         AVG(3) = 129.5
                   Olive oil             AVG(3) = 91.2
                   Cooking butter        AVG(3) = 32.4
                   Margarine             AVG(3) = 79.0

Figures
                  The figures show a parameter report and a titration curve (sunflower oil) regis-
                  tered on the Titrino.
       'fm                                           'fr
       785 DMP Titrino       02287 785.0010          785 DMP Titrino      02287 785.0010
       date 1999-11-10 time 08:06       2            date 1999-11-10 time 08:06      2
       DET U             IodNo                       card label:Appl.751
       >calculations                                 U(init)     -84 mV DET U    IodNo
       IN=(C30-EP1)*C01/C00;2;g/g                    smpl size 0.123 g
       C00=           0.123                          EP1        36.191 ml      75 mV
       C01=           1.269                          IN       131.63 g/g
       C30=          48.949                          stop V reached
             ============                                ============

       'pa
       785 DMP Titrino        02287 785.0010         stop U            OFF mV
       date 1999-11-10 time 08:06        2            stop EP             9
       DET U             IodNo                        filling rate     max. ml/min >statistics
       parameters                                     status:          OFF
       >titration parameters                         >evaluation
         meas.pt.density        4                     EPC                5
         min.incr.        10.0 µl                     EP recognition:      all
         dos.rate          max. ml/min                fix EP1 at U       OFF mV
         signal drift      20 mV/min                  pK/HNP:            OFF
         equilibr.time       38 s                    >preselections
         start V:         OFF                         req.ident:        OFF
         pause              0s                        req.smpl size:      all
         meas.input:          1                       limit smpl size:   OFF
         temperature         25.0 °C                  activate pulse:     OFF
       >stop conditions                                      ============
         stop V:          abs.
         stop V            42 ml
                                     Application Bulletin                              No. 141/3 e
Analysis of edible oils and fats                                                            Page 6




4. Determination of the peroxide number


Apparatus and accessories
                As described under 3. (IN). Additional exchange unit(s)

Reagents

                • Titrant: c(Na2S2O3) = 0.01 or 0.001 mol/L (prepared fresh daily from a 0.1 mol/L
                  solution)
                • Solvent mixture: glacial acetic acid / 1-decanol 3:2, contains 20 ... 30 mg/L io-
                  dine
                • Potassium iodide: saturated solution in dist. H2O (stored in a dark bottle)


Analysis
                According to the expected peroxide number, weigh 1 ... 2 g of the sample in a
                glass beaker and dissolve with 10.0 mL solvent mixture, then add 200 µL potas-
                sium iodide. Shake well and allow to stand for about 1 minute in a dark place. After
                addition of 50 mL dist. H2O, titrate the formed iodine with thiosulphate ( c = 0.01
                resp. 0.001 mol/L). A blank control sample should be prepared and treated the
                same way. Store the result as the Common Variable C30 in the instrument.

Calculations
                Peroxide number PON (meq. O2 / kg) = C01 * (EP1 - C30) * C02 / C00

                C00 = sample weight in g
                C01 = 10 when using 0.01 mol/L and
                        1 when using 0.001 mol/L thiosulphate
                C02 = titer of the used thiosulphate solution
                C30 = mL thiosulphate for the blank
                EP1 = mL thiosulphate for the sample

Remarks
                • Use of a chlorinated solvent (chloroform) was avoided in this method also.
                  Comparisons displayed a good agreement of the results.
                • A small quantity of iodine was purposely added to the solvent mixture to enable
                  the determination of a useable blank value. A condition for this is, however, that
                  the exact same amount (10.0 mL) of solvent mixture be used for the determina-
                  tion of both the blank and the sample.
                • Samples with peroxide numbers under 1 are titrated with c(thiosulphate) = 0.00l
                  mol/L. A greater use of titrant results in a better reproducibility.
                • The used solvent mixture is cheaper and, above all, easier to dispose of than
                  corresponding mixtures with chloroform. In addition, only a fifth of the otherwise
                  required amount of solvent is used with the method described above.
                                        Application Bulletin                               No. 141/3 e
Analysis of edible oils and fats                                                                Page 7

Results
                     Olive oil             AVG(5) = 8.63      0.05
                     Sunflower oil A       AVG(5) = 0.18      0.01
                     Sunflower oil B       AVG(5) = 0.07      0.008

Figures

                   The figures show a parameter report and a titration curve (thistle oil), registered
                   on the Titrino.
'fm                                                  'fr
785 DMP Titrino      02287 785.0010                  785 DMP Titrino      02287 785.0010
date 1999-11-01 time 15:57      9                    date 1999-11-01 time 15:57      9
DET U           Perzahl                              card label:Appl.751
>calculations                                        U(init)     -82 mV DET U Perzahl
POZ=C01*(EP1-C30)*C02/C00;2;meq/kg                   smpl size 1.923 g
C00=          1.923                                  EP1         8.596 ml      12 mV
C01=           0.01                                  POZ         42.62 meq/kg
C02=           1000                                  stop V reached
C30=            0.4                                           ============
              ============


'pa
785 DMP Titrino        02287 785.0010
date 1999-11-01 time 15:57        9                  >statistics
DET U           Perzahl                               status:          OFF
parameters                                           >evaluation
>titration parameters                                 EPC               5
  meas.pt.density        4                            EP recognition:     all
  min.incr.        10.0 µl                            fix EP1 at U      OFF mV
  dos.rate         max. ml/min                        pK/HNP:           OFF
  signal drift      50 mV/min                        >preselections
  equilibr.time       26 s                            req.ident:       OFF
  start V:         OFF                                req.smpl size:     all
  pause              0s                               limit smpl size:  OFF
  meas.input:          1                              activate pulse:    OFF
  temperature         25.0 °C                                  ============
>stop conditions
  stop V:          abs.
  stop V            15 ml
  stop U            OFF mV
  stop EP             9
  filling rate    max. ml/min
                                     Application Bulletin                                No. 141/3 e
Analysis of edible oils and fats                                                               Page 8



5. Determination of the saponification number


Apparatus and accessories

                • Instruments as described under 3. (IN).
                • Exchange unit (ev. PP reagent bottle 6.1608.040)
                • Solvotrode 6.0229.100, electrolyte c(TEA-Br) = 0.4 mol/L in ethylene glycol,
                  6.2320.000


Reagents

                • c(KOH) = 0.5 mol/L in ethanol
                • c(HCl) = 0.5 mol/L
                • Ethanol


Analysis
                Weigh out approx. 2 ... 5 g of the sample substance to within +/- 0.005 g in a
                round-bottomed flask. Add 25.0 mL KOH and a magnetic stirring bar. Attach the re-
                flux cooler, heat up and boil gently for 30 minutes, tilting the flask back and forth
                now and then.
                After cooling, dilute the flask contents sufficiently with ethanol, insert electrode and
                burette tip, then back-titrate the KOH excess with HCI. A blank control sample
                should be prepared and treated the same way. Store the result as the Common
                Variable C30 in the Titrator.


Calculations
                Saponification SN (mg/g KOH) = (C30 - EP1) * C01 / C00

                C00 = sample weight in g
                C01 = 28.053 (equivalent weight KOH)
                C30 = mL HCl for the blank
                EP1 = mL HCl for the sample

Results

                  Sunflower oil        AVG(3) = 190.7
                  Olive oil            AVG(3) =192.3
                  Cooking butter       AVG(3) = 231.1
                  Margarine            AVG(3) = 118.4
                                        Application Bulletin                             No. 141/3 e
Analysis of edible oils and fats                                                             Page 9

Figures
                   The figures show a parameter report and a titration curve (Margarine) registered
                   on the Titrino.

'fm                                                'fr
785 DMP Titrino      02287 785.0010                785 DMP Titrino      02287 785.0010
date 1999-11-03 time 09:23      3                  date 1999-11-03 time 09:23       3
DET U            Sapno.                            card label:Appl.751
>calculations                                      U(init)     -375 mV DET U    Sapno.
SN=(C30-EP1)*C01/C00;2;mg/g                        smpl size 2.005 g
C00=           2.005                               EP1         8.198 ml     -168 mV
C01=          28.053                               EP2        24.811 ml      242 mV
C30=          24.682                               SN         230.64 mg/g
               ============                        stop V reached
                                                            ============



'pa
785 DMP Titrino        02287 785.0010
date 1999-11-03 time 09:23        3                >statistics
DET U            Sapno.                             status:          OFF
parameters                                         >evaluation
>titration parameters                               EPC               5
  meas.pt.density        4                          EP recognition:     all
  min.incr.        10.0 µl                          fix EP1 at U      OFF mV
  dos.rate         max. ml/min                      pK/HNP:           OFF
  signal drift      50 mV/min                      >preselections
  equilibr.time       26 s                          req.ident:       OFF
  start V:         OFF                              req.smpl size:     all
  pause              0s                             limit smpl size:  OFF
  meas.input:          1                            activate pulse:    OFF
  temperature         25.0 °C                                ============
>stop conditions
  stop V:          abs.
  stop V            30 ml
  stop U            OFF mV
  stop EP             9
  filling rate    max. ml/min
                                     Application Bulletin                              No. 141/3 e
Analysis of edible oils and fats                                                           Page 10



6. Determination of the acid number, degree of acidity
   and free fatty acids (FFA)


Apparatus and accessories
                As described under 5. (SN).
                • Exchange unit (ev. with PP reagent bottle 6.1608.040)


Reagents

                • c(KOH) = 0.1 mol/L in isopropanol
                • Solvent mixture: ethanol/diethyl ether 1 : 1 (neutralised with KOH against phe-
                  nolphthalein).


Analysis
                Weigh out accurately approx. 5 ... 10 g moisture-free oil or melted fat in a beaker,
                dissolve in 50 mL solvent mixture and titrate with KOH.


Calculations

                • RS1; Acid number AN (mg/g KOH) = EP1 * C01 / C00
                • RS2; Degree of acidity (mL KOH, c = 1 mol/L pro 100 g) = EP1 * C02 / C00
                • RS3; Free fatty acids (FFA) = RS1 * C03 / C04

                C00 = sample weight in g
                C01 = 5.61 (equivalent weight KOH)
                C02 = 10
                C03 = Mr corresponding acid in g/mol*
                C04 = 561 (equivalent weight KOH)
                EP1 = mL c(KOH) = 0.1 mol/L
                RS1 = acid number
                * Mr Oleic acid = 282 g/mol
                  Mr Palmitic acid = 256 g/mol (palm oil)
                  Mr Lauric acid = 200 g/mol (coconut oil, palm-nut fat)
                  Mr Erucic acid = 338 g/mol (Colza oil)

                If the hydroxyl number should also be determined in the same sample, the acid
                number (RS1) is additionally stored as the Common Variable C31.

Results

                  Colza oil    AVG(3) = 0.07
                  Olive oil    AVG(3) = 0.64
                  Margarine    AVG(3) = 0.22
                                        Application Bulletin                               No. 141/3 e
Analysis of edible oils and fats                                                              Page 11

Figures
                   The figures show a parameter report and a titration curve (Colza oil) registered on
                   the Titrino.

'fm                                                 'fr
785 DMP Titrino       02287 785.0010                785 DMP Titrino       02287 785.0010
date 1999-11-12 time 08:42       6                  date 1999-11-12 time 08:42        6
DET U               SZ                              card label:Appl.751
>calculations                                       U(init)     -75 mV DET U       SZ
SZ=EP1*C01/C00;2;mg/g                               smpl size 9.675 g
SG=EP1*C02/C00;2;ml                                 EP1         0.047 ml      -117 mV
FFA=RS1*C03/C04;2;                                  EP2         0.118 ml      -225 mV
C00=          9.675                                 SZ          0.03 mg/g
C01=           5.61                                 SG          0.05 ml
C02=             10                                 FFA          0.03
C03=            338                                 stop V reached
C04=            561                                         ============
              ============


'pa
785 DMP Titrino        02287 785.0010
date 1999-11-12 time 08:42        6                 >statistics
DET U               SZ                               status:          OFF
parameters                                          >evaluation
>titration parameters                                EPC               5
  meas.pt.density        4                           EP recognition:     all
  min.incr.        10.0 µl                           fix EP1 at U      OFF mV
  dos.rate         max. ml/min                       pK/HNP:           OFF
  signal drift      20 mV/min                       >preselections
  equilibr.time       38 s                           req.ident:       OFF
  start V:         OFF                               req.smpl size:     all
  pause              0s                              limit smpl size:  OFF
  meas.input:          1                             activate pulse:    OFF
  temperature         25.0 °C                              ============
>stop conditions
  stop V:          abs.
  stop V             2 ml
  stop U            OFF mV
  stop EP             9
  filling rate    max. ml/min
                                     Application Bulletin                                No. 141/3 e
Analysis of edible oils and fats                                                              Page 12



7. Determination of the hydroxyl number


Remarks
                The most frequently described method for the determination of the hydroxyl num-
                ber is the reaction with acetic acid anhydride in pyridine and following KOH titration
                of the formed acetic acid. This method has, however, some major disadvantages:
                • Small hydroxyl numbers (common in edible oils) cannot be determined accu-
                   rately.
                • It must be boiled for 1 h in the reflux apparatus and converted, which is time
                   consuming.
                • The method cannot be automated.
                • Poisonous pyridine is used.
                These are significant reasons for the use of the easier and more exact method ac-
                cording to ASTM E 1899-97 described here.
                The (primary and secondary) hydroxyl groups are converted to an acidic car-
                bamate with toluol-4-sulfonyl-isocyanate at room temperature. This is then titrated
                (non-aqueous) with tetrabutyle ammonium hydroxide (TBAOH).


Apparatus and accessories

                • As described under 5. (SN).

Reagents

                • Titrant: c(TBAOH) = 0.1 mol/L in isopropanol/methanol (Merck No. 109162)
                • Reaction solution (TSI)
                  Pour approx. 250 mL acetonitrile into a 500 mL measuring flask and add 20 mL
                  toluol-4-sulfonyl-isocyanate (e.g. Fluka No. 89815). Fill up to the mark with ace-
                  tonitrile and mix. The reaction solution is stable for approx. 1 month.
                • Solvent: Acetonitrile, HPLC quality and toluol p.a.


Analysis
                According to the expected hydroxyl value, weigh out 0.1 ... 15 g sample** into a
                beaker and mix with 3 mL toluol and 7 mL acetonitrile. Add 10.0 mL reaction solu-
                tion, cover with a watch glass and, while slightly stirring, allow to react for 5 min-
                utes at room temperature. Add 0.5 mL dist. H2O and, stirring slightly, allow to react
                again for 5 minutes. The excess of reaction solution is destroyed. After addition of
                30 mL acetonitrile, titrate up to after the second end point with c(TBAOH) = 0.1
                mol/L. After each titration, rinse first with acetone, then stirring slightly with dist.
                H2O and set the electrode for 1 min in dist. H2O.

                **   The ideal sample weight is calculated as follows:
                     g sample = 40 / expected OHV
                                        Application Bulletin                            No. 141/3 e
Analysis of edible oils and fats                                                              Page 13

Calculations
                   Hydroxyl value OHV in mg/g KOH
                   OHV = (EP2 - EP1) x C01 x C02 / C00
                   C00 = sample weight in g
                   C01 = 56.1 (Mr KOH in g/mol)
                   C02 = 0.1 (concentration TBAOH in mol/L)

Figures
                   The figures show a parameter report and a titration curve (785 Titrino).
                     'fm
                     785 DMP Titrino      02287 785.0010
                     user                ng
                     date 2000-06-27 time 09:23      2
                     DET U              OHZ
                     >calculations
                     OHZ=(EP2-EP1)*C01*C02/C00;2;mg/g
                     C00=          0.498
                     C01=           56.1
                     C02=            0.1
                               ============

'pa
785 DMP Titrino        02287 785.0010                stop U               OFF mV
user            ng                                   stop EP                9
date 2000-06-28 time 14:29        2                  filling rate        max. ml/min
DET U           Method15                            >statistics
parameters                                           status:             OFF
>titration parameters                               >evaluation
  meas.pt.density        4                           EPC                   5
  min.incr.        10.0 µl                           EP recognition:         all
  dos.rate         max. ml/min                       fix EP1 at U          OFF mV
  signal drift      20 mV/min                        pK/HNP:               OFF
  equilibr.time       38 s                          >preselections
  start V:         OFF                               req.ident:           OFF
  pause              0s                              req.smpl size:         all
  meas.input:          1                             limit smpl size:      OFF
  temperature         25.0 °C                        activate pulse:        OFF
>stop conditions                                            ------------
  stop V:          abs.
  stop V            20 ml
                                    Application Bulletin                             No. 141/3 e
Analysis of edible oils and fats                                                         Page 14



8. Determination of nickel traces by polarography


Apparatus and accessories

                • VA Computrace or
                • VA Trace Analyzer with VA Stand


Reagents
                Only high quality reagents and high purity water are used.
                • w(HCl) = 30 %
                • w(NH3) = 25 %
                • w(Dimethyl glyoxime) = 1 % in ethanol; freshly prepared daily
                • Ni-standard: ρ Ni) = 100 mg/L (1 mL = 0.1 mg Ni+2)


Sample preparation
                Weigh out accurately 2.5 g sample in a round-bottomed flask. Add 2.5 mL HCl and
                heat to boiling in the reflux apparatus for 15 minutes. Rinse out the warm solution
                with a small quantity of high purity water into a separating funnel and run off the
                aqueous phase. Extract the fatty phase and the round-bottomed flask three times
                with hot high purity water. Now filter the combined aqueous extracts through a pa-
                per filter (e.g. S&S 5892) into a 100 mL measuring flask, add 5 mL NH3 and fill up
                to the mark with high purity water.

Analysis
                Pipette out 20 mL of the prepared sample solution (corresponding to a 0.5 g por-
                tion of the original sample) into the polarography vessel and deaerate for 5 minutes
                with nitrogen. Add 20 µL dimethyl glyoxime, briefly deaerate once again and record
                the DP polarogramm under following conditions:
                         Working electrode          SMDE
                         Mode                       DP
                         Amplitude                  - 50 mV
                         U start                    - 0.8 V
                         U stop                     - 1.4 V
                         Peak potential             ca. - 1.12 V

                The quantitative analysis is made using the standard addition method (add twice 1
                µg Ni each time).
                The blank value of the reagents should be determined the same way and sub-
                tracted from the result.

Remark

                • Incineration as decomposition is unsuitable because volatile nickel carbonyl is
                  lost in the process.
                                                                 Application Bulletin                                           No. 141/3 e
Analysis of edible oils and fats                                                                                                    Page 15

Figures
                                  The figures show a nickel determination in margarine registered on the VA Com-
                                  putrace 757.
                            N i in M a r g a r in e                              Ni
                              M a rg a rin e N i                                 c =           0.402           ppm
                                                                                 +/-           0.003           ppm    (0.81%)
         -300n
                                         Ni


         -250n
                                                                                          -1 5 0 n



         -200n
i (A)




                                                                                          -1 0 0 n




                                                                              i (A)
         -150n

                                                                                         -5 0 . 0 n

         -100n
                                                                                         -1 .1 e -0 0 5
                                                                                                    0
                                                                                       -2 0 . 0 u       0   20.0u 40.0u 60.0u 80.0u 100u
                 - 0 .9 0     - 0 .9 5    - 1 .0 0    - 1 .0 5   - 1 .1 0
                                           E (V )                                                               c / ( g /l)

==================== METROHM 757 VA COMPUTRACE (5.757.0010) ====================
 Determ.     : 10181050_Ni in Margarine.dth
 Date        : 1999-10-18             Time: 10:50:57
 Modified    : 1999-10-18 13:12:08    User:               Cell volume: 20.100 ml
--------------------------------------------------------------------------------
  Ident                                                            Sample volume
  Margarine Ni                                                         20.000 ml
--------------------------------------------------------------------------------
 Method : Ni in Margarine.mth
 Title   : Ni in Margarine
 Remark1 :
 Remark2 :
--------------------------------------------------------------------------------
  Substance : Ni                                             Comments
  Mass conc.:   10.807 ug/l                                  ------------------
  MC.dev.   :    0.087 ug/l       (    0.81%)
  Mass      : 217.221 ng
  Add.mass :     1.000 ug

                              VR           V         nA             i.mean    Std.Dev. i.delta                   Comments
                             ----        -----       ------         ------    ------- -------                    ------------------
                             1-1         -0.990       -18.3         -18.2     0.129
                             1-2         -0.990       -18.2
                             2-1         -0.990      -103.6         -103.4    0.248          -85.2
                             2-2         -0.990      -103.3
                             3-1         -0.990      -187.0         -186.9    0.162          -83.5
                             3-2         -0.990      -186.8

   Substance                  Calibr.                Y.reg/offset            Slope                  Nonlin.              Mean deviat.
   ---------                  --------               ------------            ----------             ----------           ------------
         Ni                   std.add.                -1.834e-008           -1.697e-003                                    1.257e-010

 Solutions
--------------------------------------------------------------------------------

        No. Content                                          Vol. (ml) Predose (ml)
        --- ------------------------------------------------ --------- --------------

   Final results                                                            +/- Res. dev.   %                    Comments
   ---------------------------------                                        ------------------                   ------------------
           Ni =       0.402 ppm                                             0.003        0.807
                                     Application Bulletin                              No. 141/3 e
Analysis of edible oils and fats                                                           Page 16

Literature
                Water content
                • AOAC 984.20 (1990)
                  Moisture in oils and fats. Karl Fischer method
                • ISO 760-1978
                  Animal and vegetable fats and oils. Determination of water - Karl Fischer
                  method (General method)
                • ISO 8534-1996
                  Animal and vegetable fats and oils - Determination of water content - Karl
                  Fischer method
                Oxidative stability
                • 2.4.28.2-93 (1993)
                  Fat stability test on autoxidation. CDM (Conductimetric determination method)
                  Japanese norm (in Japanese)
                • AOCS Cd 12b-92 (1992)
                  Sampling and analysis of commercial fats and oils. Oil Stability Index (OSI)
                • ISO 6886: 1996
                   Animal and vegetable fats and oils - Determination of oxidation stability (accel-
                   erated oxidation test)
                Iodine value
                • AOCS Cd 1-25 (1988)
                  Sampling and analysis of commercial fats and oils. Iodine value. Wijs method
                • ISO 3961: 1989
                  Animal and vegetable fats and oils - Determination of iodine value
                Peroxide value
                • AOCS Cd 8-53 (1986)
                  Sampling and analysis of commercial fats and oils. Peroxide value
                • ISO 3960-1977
                  Animal and vegetable fats and oils - Determination of peroxide value
                • ISO 3976: 1977
                  Anhydrous milk fat - Determination of peroxide value (reference method)
                Saponification value
                • AOCS Cd 3-25 (1973)
                  Sampling and analysis of commercial fats and oils. Saponification value
                • ISO 3657: 1988
                  Animal and vegetable fats and oils - Determination of saponification value
                Acid value, acidity, free fatty acids
                • AOCS Cd 3a-63 (1987)
                  Sampling and analysis of commercial fats and oils. Acid value
                • ISO 660-1983
                  Animal and vegetable fats and oils - Determination of acid value and of acidity
                • ISO 1242: 1973
                  Essential oils - Determination of the acid value
                • AOCS Ca 5a-40 (1987)
                  Sampling and analysis of commercial fats and oils. Free fatty acids
                Hydroxyl value
                • AOCS Cd 13-60 (1988)
                  Animal and vegetable fats and oils. Hydroxyl value

				
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Description: No. 141/3 e Application Bulletin