Applications of arsine evolution methods to environmental analyses

Because of its biological activity, arsenic is involved in an active global geochemical cycle. Arsenic has been found to be transferred to the atmosphere, at least in part, by evolution of trimethyl arsine and similar methyl arsenic compounds. Because of the environmental importance of the several arsenic forms [inorganic arsenic (III) and (V), methylarsonic acid, dimethylarsenic acid, trimethylarsine, methylarsine, and dimethylarsine], chemical methods for their analysis are needed. Sensitive methods are required because environmental concentrations encountered are generally in the range of 0.01 (or lower) to 3 ppb for natural waters and 1-6 ng As/m3 for arsenic in air. Arsine evolution by pH selective reduction permits specific analyses for inorganic As (III) and As (V). Methylarsenic acids may be reduced to corresponding methylarsines with sodium borohydride after which separation permits specific detection of these arsenic compounds. The most sensitive and selective methods combine reduction, separation, and emission type detectors. The intensity of arsenic atomic emission lines is observed. This type of detector provides a lower limit of detection down to 0.02 ng As per sample. The methods have been applied to a variety of environmental samples.