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United States Department of Agriculture

Agricultural Research Service

Title: Liquid-Liquid Extraction of Cadmium by Sodium Diethyldithiocarbamate from Biological Matrices for Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

Authors
item Vanderpool, Richard
item Buckley, Wayne - BRANDON RESEARCH STATION

Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 1998
Publication Date: N/A

Interpretive Summary: The adverse effect of cadmium intake on the health of individuals in exposed populations is well known. There is now a growing concern about the long term effects, on human health, from low concentrations of cadmium. Human absorption of cadmium from food is thought to be 10% of their total cadmium intake. However, some animal studies imply that cadmium absorption may be much lower. Documentation of lower human cadmium absorptions may result in lower estimations of cadmium's hazards, both in the general and exposed populations. We would like to measure cadmium absorption in humans by using stable cadmium isotopes and an instrumental technique called IDICPMS. Using the IDICPMS technique, human cadmium absorption could be measured by monitoring cadmium isotopes in human feces. Unfortunately, there is not a good IDICPMS procedure for measuring cadmium in feces. We have developed and tested a procedure for measuring cadmium in biological matrices and human feces using stable cadmium isotopes and IDICPMS. After digestion, biological samples are extracted by using a chemical compound that binds to cadmium. This extraction removes cadmium from other elements that interfere with its analysis by IDICPMS. The method was successfully tested on 13 National Institute of Science and Technologies standard reference materials and human feces. This IDICPMS procedure will allow us to conduct studies with humans to measure the absorption of cadmium by humans from food.

Technical Abstract: A published procedure for the liquid-liquid extraction of Cd by NaDDC was modified and tested on 12 biological matrices of plant and animal origin for use with IDICPMS. The tested matrices were reference materials, certified for Cd, and an in-house feces standard. The digested and extracted standards were analyzed for Cd stable isotopes by ICPMS and the resulting isotope ratios examined for isobaric and polyatomic interferences. Cadmium recoveries, after extraction, ranged from 73% to 20% and apparently were to be inversely related to Cd concentration, even in the presence of excess chelator. For each reference material, the measured isotope ratios for Cd were corrected for instrumental bias, and compared to natural abundance Cd isotope ratios. Non-extracted samples had large isotope ratio deviations for all but one or two ratios. Extraction improved all the isotope ratios measured (lowered % error relative to natural abundances), but interferences were noted for a few samples. The extracted in-house human feces standard was found to have Sn signals reduced by 300-fold, but residual Sn concentrations still interfered with 116**Cd, though not 112**Cd or 114**Cd. Thus, evaluation of the NADDC-extracted in-house fecal standard and NIST reference materials indicate the successful removal of interferences that otherwise prevented accurate determinations of Cd by IDICPMS, and that a number of Cd isotope ratios could be accurately measured (<1.5% error) for multiple stable isotope tracer studies in a broad range of NaDDC-extracted biological matrices.

Last Modified: 11/27/2014
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