Speciation of six arsenic compounds using capillary electrophoresis-inductively coupled plasma mass spectrometry

Abstract

Capillary electrophoresis (CE) was used to separate four anionic {arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid and dimethylarsinic acid} and two cationic forms (arsenobetaine and arsenocholine) of As in a single run. At sufficiently high concentrations, the determination of these compounds could be accomplished by means of UV detection. The determination of low concentrations (<10 µg l ^–1 ) of these compounds of interest was accomplished by coupling CE on-line with inductively coupled plasma mass spectrometry (ICP-MS). To accomplish this coupling, a microconcentric nebulizer was used. The modifications necessary to make a conventional CE system compatible with ICP-MS, the optimization of the operation parameters and of sample stacking conditions together with the effect of the sheath liquid and of an induced laminar flow are discussed. The analytical figures of merit of the method were assessed and the limit of determination (based on the peak height of a peak for which the signal-to-noise ratio is 10:1) was found to be 1-2 µg l ^–1 As for each species. The recovery for the compounds of interest was determined using a spiked mineral water sample. Samples of mineral water, soil leachate and urine were analyzed with the CE-ICP-MS combination.