SUBSTOICHIOMETRIC SPECIATION FOR INORGANIC ARSENIC AND METHYLATED ARSENIC AND ITS APPLICATION TO SAMPLES OF MARINE ORGANISMS

A substoichiometric isotope-dilution method is described for the determination of monomethylarsonate, MeAs(V), and dimethylarsinate, Me2As(V). After the separation of MeAs(V) and Me2As(V) by extraction as their iodides into benzene, these methylated arsenic species are complexed with a substoichiometric amount of diethyldithiocarbamate in benzene, and the uncomplexed methylarsenic species are removed. The relative standard deviations for the substoichiometric extraction of MeAs(V) and Me2As(V) are 0.55% and 1.1%, respectively. This substoichiometric speciation of methylated arsenic together with an earlier substoichiometric method for speciation of inorganic arsenic species was applied to the speciation of arsenic in an acid-digested solution of a macro-algae sample. It was demonstrated that almost all the arsenic in this solution was Me2As(V) even after the digestion with nitric acid. © 1990.