Sequential spectrophotometric determination of inorganic arsenic(III) and arsenic(V) species

Abstract

The silver diethyldithiocarbamate spectrophotometric procedure for the determination of arsenic has been modified to perform the differential determination of inorganic arsenic(III) and arsenic(V) species. Based on pH control of the reduction characteristics of the borohydride ion, arsine is generated at pH 6 from arsenic(III); following acidification, arsine is then generated and trapped from arsenic(V) species. The procedure is appropriate to the determination of 2–40 µg of each arsenic species. Antimony(III), bismuth(III), chromium(VI), copper(II), gold(III), nickel(II), platinum(IV), silver(I), tellurium(IV) and tin(II) interfere in the determination of arsenic(III) and “methylarsenic” and “dimethylarsenic” species, platinum(IV) and silver(I) interfere in the determination of arsenic(V). Interference effects due to platinum can be masked by the addition of 1,10-phenanthroline to the reductant mixture. Interference due to bismuth, copper, gold, nickel, silver, tellurium and tin can be overcome by preliminary extraction of the interferents from the sample as their dithizonates.