Liquid-liquid extraction of cadmium by sodium diethyldithiocarbamate from biological matrixes for isotope dilution inductively coupled plasma mass spectrometry.

A published procedure for the liquid-liquid extraction of Cd by sodium diethyldithiocarbamate (NaDDC) was modified and tested on 12 biological matrixes of plant and animal origin for use with isotope dilution (ID) inductively coupled plasma mass spectrometry (ICPMS). The tested matrixes were reference materials, certified for Cd, and a feces in-house 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 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. Nonextracted 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 human in-house feces standard was found to have Sn signals reduced by 300-fold, but residual Sn concentrations still interfered with 116Cd, though not 112Cd or 114Cd. Thus, evaluation of the NADDC-extracted in-house fecal standard and reference materials indicate the successful removal of interferences that otherwise prevented accurate determinations of Cd by IDICPMS and show 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 matrixes.