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THE LIBERATION OF ARSENOSUGARS FROM MATRIX COMPONENTS IN DIFFICULT TO EXTRACT SEAFOOD SAMPLES UTILIZING TMAOH/ACETIC ACID SEQUENTIALLY IN A TWO-STAGE EXTRACTION PROCESS
Citation:
Parks, A N., P A. Gallagher, C A. Schwegel, A H. Ackerman, AND J T. Creed. THE LIBERATION OF ARSENOSUGARS FROM MATRIX COMPONENTS IN DIFFICULT TO EXTRACT SEAFOOD SAMPLES UTILIZING TMAOH/ACETIC ACID SEQUENTIALLY IN A TWO-STAGE EXTRACTION PROCESS. Presented at 2003 European Winter Conference on Plasma Spectrochemistry, Garmisch-Partenkirchen, Germany, January 12-17, 2003.
Impact/Purpose:
To develop an arsenic speciation protocol for the analysis of dietary components and composite diets in order to provide a more accurate assessment of human exposure to arsenicals.
Description:
Sample extraction is one of the most important steps in arsenic speciation analysis of solid dietary samples. One of the problem areas in this analysis is the partial extraction of arsenicals from seafood samples. The partial extraction allows the toxicity of the extracted arsenicals to be determined but the unextracted fraction's toxicity can not be determined. This inability to determine the toxicity of the unextracted arsenicals creates a relatively large source of uncertainty in estimating the risk from seafood exposures. Seafood exposures can produce a relatively large source of uncertainty because the arsenic concentrations in seafoods can be orders of magnitude higher than those associated with other food groups and therefore, a small error in quantitating toxicity (unextracted arsenicals imply unknown toxicity) in seafoods produces larger uncertainties in the overall exposure assessment. An additional problem can be generated by non-quantitative extractions in which the extraction solvent preferentially removes the non-toxic species while leaving the toxic species unextracted. The interpretation of these data would be that the sample contains only non-toxic arsenicals when in reality the extraction solvent has selectively removed only the non-toxic species. In this case the solvent selectivity produces an analytical negative bias which underestimates the concentration of the toxic arsenicals. Thus, a quantitative extraction is needed to minimize the unextractable arsenicals (which should provide the maximum species specific information) and eliminate the question about analytical bias induced by solvent selectivity (since all the arsenic is accounted for).
This presentation will focus on the use of tetramethylammonium hydroxide (TMAOH) as an extraction solvent for difficult-to-extract seafoods. The extraction utilizes a 0.83% TMAOH extraction solvent which is heated in a convection oven at 60oC for 3hrs. The sample is then neutralized with acetic acid to remove proteins and returned to the oven for 21hrs at 80oC. Data will be presented which indicates that the neutralization step is essential because arsenosugars are converted during this process from an unchromatographable species to a chromatographable species. Chromatographic and total arsenic data will be presented to document this conversion. Finally, chromatographic data will be summarized utilizing the two-stage (base followed by acid) extraction procedure.