021 determination of cadmium

Document Sample
021 determination of cadmium Powered By Docstoc
					                      KMITL Sci. J. Vol.8 No.2 (Section B)     July – December, 2008



DETERMINATION OF CADMIUM IN RICE BY RADIOCHEMICAL
          NEUTRON ACTIVATION ANALYSIS

                                                    
           Arunee Promsawad1, Arunee Kongsakphaisal1 and Sirinart Laoharojanaphand 2
              1
               Department of Chemistry, Faculty of Science, King Mongkut’s Institute of
                           Technology Ladkrabang, Bangkok 10520 Thailand.
      2
        Thailand Institute of Nuclear Technology (Public Organization), Nakornnayok, Thailand.


                                              ABSTRACT

The determination of cadmium in rice by Radiochemical Neutron Activation Analysis (RNAA) is the main
objective of this research. Cadmium were separated from interfering by anion exchange resin. Optimum
absorption and elution condition were studied. The absorption of cadmium on the resin was obtained by
using 2 M HCl. The eluting condition of cadmium was using 8 M ammonia solution with the eluting
efficiency of 96 %. The detection limit was 6 g kg-1 (n = 5). The accuracy of the analysis of SRM 1577b
(Bovine liver) (NIST) was 92 % recovery (n = 7). The results indicated that the present method was used to
determine cadmium concentration in rice form Tak Province and the other parts of Thailand, which were
found in the range 7.4-343.4 g.kg-1 and 6.5-16.0 g.kg-1, respectively.

KEYWORDS : Rice,Cadmium, Ion exchange chromatography,                  Radiochemical Neutron Activation
           Analysis.


                                          1. INTRODUCTION

Cadmium is one of the main elemental pollutants in the environment due to its increased utilization in the
industry and atmospheric. Its toxicology is hazardous for aquatic, animal and plant life. Food is a pathway
of contamination. In man or animal the metal is mainly accumulated in kidney and liver with long
biological half life [1][2].
         Separation of inorganic ions by ion exchange chromatography technique is often employed in
radiochemical NAA as well. Numerous separation procedures are almost exclusively based on the use of
mono functional ion exchange, mostly strong basis and strong acidic ion exchange resin [3][4][5][6].
         The development of trace element analysis techniques to determine trace element is very important
for analyzing various biological materials have gradually stimulated the interest of biological,
environmental behavior of trace elements, especially while evaluating the extent of assure sufficient
accuracy for cadmium determination at trace concentration level, namely AAS, ICP-AES and ICP-MS.
Neutron activation analysis (NAA) in the accurate and precise elemental analysis of biological materials is
prominent, despite the advent of several competing multi-element analytical techniques. Neutron activation
analysis with radiochemical separation (RNAA) combines characteristics of accuracy and precision with
high sensitivity [7][8][9][10][11].
         This paper describes the system developed enable for the determination of cadmium in rice by
Neutron activation analysis with radiochemical separation (RNAA). The method is extended and improved
version of that described earlier [1]. In this paper, the aspects of sample preparation, neutron irradiation,
gamma spectrum evaluation contribution are also discussed.





    Corresponding Author. Tel. 02-326-4339-53 ext. 223, Fax. 0-2326-4354.
                          E-mail: kkarunee@kmitl.ac.th.
                       KMITL Sci. J. Vol.8 No.2 (Section B)     July – December, 2008


                                  2. MATERIALS AND METHODS

2.1 Reagent
Standard solutions were prepared by dissolving appropriate amounts of CdO (Merck) 99.99 % w/w in 5 %
(v/v), HNO3 (Merck).
         The calibration standard solutions were prepared by diluting cadmium standard solutions in the
range from 5 g/mL to 25 g/mL.
         The accuracy of the result from certified reference materials in Bovine Liver SRM 1577b NIST,
USA was studied.

2.2 Sample collection
        Rice samples were collected periodically along Mae Tao River, Tak province and the other parts of
Thailand.

2.3 Sample Preparation
          A 1.0 g. of sample was weighed in small polyethylene bags, pre-cleaned with nitric acid. The
standard solutions were made by spot cadmium stock solution onto a Whatman filter paper No.42 in a
circle dia.1.5 cm. After evaporation under an IR lamp the standards were packed in polyethylene bags. The
samples and standards were packed in polyethylene bags, and placed in a small piece of aluminium foil,
codified and placed in an aluminium irradiation can, irradiated for 36 hours at thermal neutron flux of
1.4x1011 n/cm2.sec at the Thai Research Reactors (TRRI/MI), Thailand Institute of Nuclear Technology
(Public Organization), Bangkok, Thailand.

2.4 Radiochemical separation
          After 2 days of cooling, the samples and standards were digested with 30 mL conc.HNO3 and
evaporated to dryness , added 10 mL HClO4(72% w/w) and evaporated to dryness, added 10 mL 30 %
H2O2 solution and 10 mL 2 M HCl and evaporated to dryness, then dissolved in 1 mL 2 M HCl , and load
through the anion exchange column with Dowex 1-X8 resin (Chloride form 100-200 mesh). The cadmium
is retained in the resin. The sodium and ion interferences are eliminated by washing with 10 mL of 2 M HCl
and finally cadmium is eluted with 10 mL 8 M NH3 solution, the  -ray spectrum measured for 180 min
with the gamma spectrometer with HpGe detector (DSA 1000 Digital Spectrum Analyzer) and a channel
analyzer were used to detect the gamma radiation of the radionuclide Cd-115, with a half life of 2.24 days,
gamma-ray energies measured at 336.02 keV., and irradiation time were 36 hour.

2.5 Gamma Radiation Measurement
          The rice samples and standard cadmium oxide (CdO) 1.42 mg were weighed in small polyethylene
bags, irradiated for 36 hours at thermal neutron flux of 1.4 x 10 11 n/cm2.sec and after 2 days of cooling, the
samples were digested, the  -ray spectrum measured for 180 min with the gamma spectrometer with HpGe
detector (DSA 1000 Digital Spectrum Analyzer) and a channel analyzer used for detection the gamma
radiation of the sample. The radionuclide, half lives, gamma-ray energies and irradiation time were show in
Table 1.

Table 1 Experimental parameter for cadmium in rice

                                                                                         Irradiation
             Element         Radionuclide          Half-life       -Energy (keV)
                                                                                        time (hour)
        Cd                  Cd-115             2.24 d              336.02              36

        The concentration of cadmium in rice samples were determined via the standard comparator
method using 336.02 keV gamma-peak from the decay of Cd-115.


                                3. RESULTS AND DISCUSSION

3.1 Adsorption and Desorption
The maximum adsorption of cadmium on the resin when using 2 M HCl was 95.2% (Table 2.). Elution
efficiency of cadmium from the column using 10 mL of 8 M NH 3 solution was 95.92 % as shown in Table
3. The elution curve of cadmium from the column was shown in Figure1.




                                                      13
                    KMITL Sci. J. Vol.8 No.2 (Section B)     July – December, 2008



Table 2 Adsorption of cadmium on the resin in HCl media.

                 Concentration of HCl, M                            Adsorption, %
                            2                                       95.20 ± 1.35
                            4                                       81.50 ± 4.19
                            6                                       41.62 ± 3.20
                            8                                       69.27 ± 5.76
                            10                                      85.69 ± 3.87


Table 3 Effect of ammonia solution on the eluting efficiency of cadmium

                  Concentration of NH3, M                    Eluting efficiency of Cd (%)
                              6                                      50.00 ± 2.99
                              8                                      95.92 ± 0.92
                             10                                      50.77 ± 1.92




                Figure 1. The elution curve of cadmium from the column by washing with
                      10 mL of 2 M HCl and eluted with 10 mL 8 M NH3 solution.

3.2 Detection limit, precision and correlation coefficient (r)
        Detection limit method [12] is defined as 3 times the standard deviation of the background (blank
sample) on which the photopeak is situated.
        So, detection limit, precision and correlation coefficient (r) of calibration curve (2 -25 g/mL)
were determined for the proposed method. The results are summarized in Table 4

Table 4 Analytical performance of RNAA for the determination of cadmium
                         Parameter                                  Cadmium
               Detection limit (g.kg-1)(n=5)                           6
                 Precision (% RSD)(n=7)                               2.66
                 Correlation coefficient (r)                         0.9996


         Detection limit of cadmium was 6 g kg-1. The precision of the standard cadmium was 2.66 % RSD
with lower than 10 %RSD. The linearity of calibration curve was 5-25 g/mL which correlation coefficient,
r more than 0.999.




                                                   14
                      KMITL Sci. J. Vol.8 No.2 (Section B)      July – December, 2008


3.3 Accuracy
        The reliable approach for assessment of the accuracy in rice analysis can be applied to cadmium
which reference values are available in the same matrix. The result for the determination of cadmium in
Table 5 is good agreement with the Certified Reference Material (CRM).

Table 5 Results for the accuracy of the analysis of cadmium in the Certified
        Reference Material (CRM) by RNAA (g g-1)(n=7)

                       Sample            Certified Value         Found Value         % recovery
                     SRM 1577b                 0.50               0.46±0.01              92
                    (Bovine liver)           (g g-1)              (g g-1)


3.4 Determination of cadmium in rice samples of Mae Tao, Tak.
           The -ray spectra from rice samples were analyzed. Typical -ray spectra of rice are shown in
Figure.2




               Figure 2 A typical -ray spectrum of rice samples at the Mae Tao, Tak, Thailand.

        Trace element of cadmium was identified and quantified using energy and peak area of cadmium.
The concentrations of trace element were calculated using standard comparison. The concentration of
cadmium in rice determined by RNAA were summarized in Table 6.
The cadmium trace element was identified and quantified using energy and peak area of cadmium. The
concentrations of trace element were calculated using standard comparison.
        The results shown that the concentration of cadmium in rice at Mae Tao, Tak province were
between 7.4-343.4 g.kg-1 and the other parts of Thailand as a control sample were between 6.5-16 g.kg-1 .
The concentration of cadmium in the Mae Tao is higher than the other regions because the contamination of
cadmium in soil due to its increased utilization in the industry in Tak province.



                                          4. CONCLUSIONS

In this study, the concentration of cadmium concentration level differences between agriculture area and
controls area. It can be used RNAA techniques for the determination of cadmium at a trace levels in food
samples and biological materials, which precision and accuracy had been proved




                                                     15
                    KMITL Sci. J. Vol.8 No.2 (Section B)       July – December, 2008




                                  5. ACKNOWLEDGEMENTS

This study was support by Thailand Institute of Nuclear Technology (PublicOrganization), Ministry of
Science and Technology and the Department of Chemistry, Faculty of Science, King’s Institute of
Technology Ladkrabang (KMITL) for providing its research facilities



Table 6. The concentration of cadmium (g.kg-1) in the rice.

                     No.                          Sample                  Average Cadmium
                                                                        concentration (g.kg-1)
                     1.                     Control sample 1                       6.5
                     2.                     Control sample 2                     LOD
                     3.                     Control sample 3                      16.0
                     4.                     Control sample 4                     LOD
                     5.                     Control sample 5                     LOD
                     6.                     Control sample 6                     LOD
                     7.                     Control sample 7                     LOD
                     8.                     Control sample 8                     LOD
                     9.                      Mae Ku Nua 1                        270.0
                     10.                     Mae Ku Nua 2                         37.6
                     11.                     Mae Ku Nua 3                         60.0
                     12.                         Pha de                          304.8
                     13.                        Pha de 1                          37.6
                     14.                        Pha de 2                         578.9
                     15.                   Mae Tao Tai Village                   343.4
                     16.                  Mae Tao Mai Village                    343.4
                     17.                  Mae Tao Klang Village                  130.7
                                                                                 194.9
                     18.                    Pha de Mae Tao
                                                                                151.7
                     19.                  Mae Tao Sun Don Chai                     7.4
                     20.                    Tum Sua Village                        8.5


                                           REFERENCES

[1]   Bedregal P.S., Montoya E.H., “Determination of Cadmium using radiochemical neutron activation
      analysis.” Journal of Radioanalytical and Nuclear Chemistry., 254,. 2002, 363-364.
[2]   Kawada T., Suzukigto S., “The use of amphoteric ion exchange resins for inorganic separations.”
      Journal of Chromatography., 150, 1991, 143-153.
[3]   Dowtali R., Jervis R.E., “Determination of trace cadmium “Determination of trace cadmium and
      other elements in bone by Epithermal Neutron Activation Analysis.” Journal of Radioanalytical and
      Nuclear Chemistry., 150, 1991, 455-463.
[4]   Aldabbgh S.S., and Dybczynski R., “ Ion Exchange behaviour of 18 elements on Amphoteric Resin
      Retardion 11A8 in Ammonium Chloride, NH4Cl+NH3 and NH4Cl+HCl media.” Journal of
      Radioanalytical and Nuclear Chemistry, Articles., 92, 1985, 37-50.
[5]   Woittiez J.R.W., and De La Cruz Tangonan M., “ Determination of Cd, Mo,Cr and Co in biological
      Materials by RNAA.” Journal of Radioanalytical and Nuclear Chemistry, Articles., 158, 1992, 313-
      321.
[6]   Zbigniew Samczynski, Rajmund Dybczynski., “Some example of the amphoteric ion exchange
      resins for inorganic separations.” Journ of Chromatography A., , 789, 1997 157-167.
[7]   Tjioe P.S., “ Extended automated separation techniques in destructive Neutron Activation Analysis ;
      application to various biological materials, including human tissue and blood. ” Journal of
      Radioanalytical and Nuclear Chemistry., 37, 1990, 511-522.
[8]   Guler Somer.,Gulbenic Guliyera.,“Simultaneous determine of copper, lead, cadmium, zinc and
      selenium in cow liver by differential pulsepolarography.” Can. J. Chem., 81:31, 2003,31-36.




                                                   16
                    KMITL Sci. J. Vol.8 No.2 (Section B)     July – December, 2008


[9]    Francesco Cubadda., Andrea Raggi., “Determination of Cadmium, lead, ion, nickel and chromium in
       selected food matrices by plasma spectrometric techniques.” Journal Microchemical., 79, 2005, 91-
       96.
[10]   Shetty P. “Determination of trace level Mercury in biological and environmental samples by Neutron
       Activation Analysis.” Journal of Radioanalytica and Nuclear Chemistry., 182:2, 1994, 205-211.
[11]   Erico Marlon de Moraes., Jose Neri Gottfried Paniz., “Cadmium determination in biological samples
       by direct solid sampling flame atomic absorption spectrometry.” Spectrochimica Acta Part B., 57,
       2002, 2187-2193.
[12]   Nomenclature in Evalution of Analytical Methods, Including Detection and Quantification
       Capabilities (IUPAC Recommendation) Pure  appl. Chem. 1995, 1699 -1723.




                                                   17

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:11/29/2011
language:English
pages:6