DETERMINATION OF ARSENATE IN AQUEOUS SAMPLES BY PRECIPITATION OF THE ARSENIC(V) MOLYBDATE COMPLEX WITH TETRAPHENYLPHOSPHONIUM CHLORIDE AND NEUTRON-ACTIVATION ANALYSIS OR HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY

Precipitation of As(V) from aqueous samples is achieved by complexation of As(V) with molybdate followed by formation of an insoluble precipitate with tetraphenylphosphonium chloride (TPP+Cl-). The selectivity of the method was studied by investigating the behaviour of other arsenic species [As(III), monomethylarsonic acid and dimethylarsinic acid] using As-73-labelled species. It follows that differentiation between As(V) and the methylated arsenic acids is excellent, but that some As(III) may precipitate. Combination with selective coprecipitation using dibenzyldithiocarbamate for preliminary As(III) removal yields accurate results when used with neutron activation analysis or hydride generation atomic absorption spectrometry. The competition of phosphate with As(V) for complexation with molybdate limits the use to samples with phosphate concentrations < 6-mu-g ml-1. Results for some real water samples are presented. The results of both detection methods are in good agreement.