Speciation of arsenic compounds by ion chromatography with inductively coupled plasma mass spectrometry detection utilizing hydride generation with a membrane separator

Abstract

Ion chromatography (IC) was used to speciate four of the environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid. Hydride generation (HG) was used to convert the species to their respective hydrides. These hydride species were detected with ICP-MS. The gas–liquid separator for the HG unit was based on microporous PTFE tubing. Two novel features which reduce noise are incorporated into the membrane-based HG unit: firstly, gas is added to the liquid stream prior to entering the membrane, and secondly, the flow of carrier gas through the gas–liquid separator forms a ‘feedback’ loop. Absolute detection limits based on 3.14σ from 7 replicates for the four arsenic species listed above were 0.6, 3.1, 1.1, and 0.7 pg, respectively. The overall IC–HG–ICP-MS system produced RSD values of 1–6% over 30 min and 2–6% over a week for the four compounds. Two saline reference materials, NASS-4 and SLEW-2 (National Research Council of Canada), were analysed to determine concentrations of the four arsenic species, and the sum of the arsenic concentration was compared with the certified total arsenic value for each of the reference materials.