Michler's thioketone is proposed as the reagent for the spectrophotometric
determination of trace arsenic(V). The molar absorptivity of the colored pr
oduct of interaction between Michler's thioketone and molybdoarsenic acid i
s (1.02 +/-0.04) x 10(5) at 640 nm. A procedure is developed for the extrac
tion-photometric determination of arsenic in tap and mineral waters. The ad
ded-found method is used. The determination limit of arsenic is 0.003 mg/L;
in the concentration range 0.008-0.12 mg/L, the relative standard deviatio
n varies from 20 to 8 %.