DECOMPOSITION OF ORGANOARSENIC COMPOUNDS BY USING A MICROWAVE-OVEN AND SUBSEQUENT DETERMINATION BY FLOW-INJECTION HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY

Environmentally important organoarsenicals such as arsenobetaine, arsenocholine and tetramethylarsonium ion do not form volatile hydrides under the commonly used analytical conditions on treatment with borohydride and it has been difficult to determine their concentrations without further derivatization. This paper describes a rapid method which completely decomposes and oxidizes these arsenicals to arsenate by using potassium persulphate and sodium hydroxide with the aid of microwave energy. The quantitative decomposition of these species permits their determination at low nanogram levels, by hydride generation atomic absorption spectrometry (HG AA). A new hydride generator which has high efficiency and minimum dead volume and therefore is suitable for flow injection analysis (FIA) is also described. A system combining flow injection analysis, on-line microwave oven digestion, and hydride generation followed by atomic absorption measurement, is developed. This system is capable of performing analysis at a sample throughput of 100-120 per hour. Calibration curves were linear from 10 to 200 ng cm-3 of arsenic and the detection limit was 5 ng cm-3 for a 100-mu-l injection or 0.5 ng of arsenic. All ten organoarsenic compounds studied gave arsenate as the decomposition product, which was confirmed by using molybdenum blue photometric measurement.