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DETECTION AND QUANTIFICATION OF A THIO-ARSENOSUGAR IN MARINE MOLLUSKS BY IC-ICP-MS WITH AN EMPHASIS ON THE INTERACTION OF ARSENOSUGARS WITH SULFIDE
Citation:
CONKLIN, S., P. A. CREED, AND JOHN T. CREED. DETECTION AND QUANTIFICATION OF A THIO-ARSENOSUGAR IN MARINE MOLLUSKS BY IC-ICP-MS WITH AN EMPHASIS ON THE INTERACTION OF ARSENOSUGARS WITH SULFIDE. Presented at 2006 Winter Conference on Plasma Spectrochemistry, Tuscan, AZ, January 08 - 14, 2006.
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:
Arsenosugars can make up a significant portion of the total arsenic in shellfish. These arsenosugars can be present in their oxide or sulfide form. IC-ICP-MS and IC-ESI-MS/MS data will be presented that indicates the presence of As(328-S) and As(328) in three species of marine mollusk. The sulfide form of the arsenosugar was found to be 12, 14 and 30% relative to the oxide in these samples. These findings initiated more fundamental studies surrounding the potential formation of arsenic sulfides during the extraction procedure. The extraction procedure of interest utilizes a tertramethylammonium hydroxide (TMAOH) solution (pH ~ 12.5) to quantitatively solubilize the arsenicals from the difficult to extract shellfish. At this point, the TMAOH extracts contain a mixture of arsenosugar oxides and sulfides. The second step utilizes acetic acid to precipitate the proteins (in order to minimize chromatographic column fouling) and produces an extract with a pH of 4. At this pH, the initial equilibrium between the oxide/sulfide favors the sulfide, but with time, the equilibrium shifts back to the oxide. This data clearly indicated that the native distribution of oxide to sulfide was influenced by the two step extraction procedure. Extractions utilizing a far less chemically aggressive 50/50 MeOH/H2O extraction fluid indicated an equilibrium that favored the oxide, but with this extraction fluid approximately 30% of the arsenic remained in the mollusk tissue. The fundamental questions raised by these results are: "What extraction parameters influence the distribution of oxide/sulfide and what co-extractant promotes an equilibrium shift towards the sulfide at low pH?".
Results will be presented that indicate that the TMAOH extraction liberates between 0.5-2 ppm sulfide. At a pH of 12, the sulfide is present as S2- and is unlikely to react with the arsenosugar oxide to produce the arsenosugar sulfide. However, the acidification of these extracts converts S2- to H2S, which reacts with the arsenosugars oxide and accounts for the conversion to the arsenosugar sulfide upon acidification. These results are significant in that extraction procedures which liberate both sulfide and arsenosugars from seafood samples are likely to produce enhanced arsenosugar sulfides if the pH is not adjusted basic to minimize the production of H2S. These findings may also extend to other arsenic oxides depending on the H2S concentrations.