Arsenic speciation: limitations with direct hydride analysis

Speciation of inorganic arsenic(III) by hydride evolution directly into an atomic-absorption system was found to be subject to error when organic forms of arsenic (such as dimethylarsinic acid) were present. Organic forms of arsenic can produce an underestimation of total arsenic when the hydride response from concentrated acid is quantitated against inorganic arsenic. Hydride responses from solutions of various acidities are reported for dimethylarsinic acid, monomethylarsonic acid, inorganic arsenic(III) and inorganic arsenic(V). Even simultaneous equations did not provide a means of resolving mixtures of the four arsenic species investigated by using direct analysis of the evolved hydrides.