Capillary electrophoresis of arsenic compounds with indirect fluorescence detection

A capillary electrophoresis (CE)-indirect fluorescence detection method for arsenic compounds is described. The five arsenic species, viz., arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), dimethylarsinate (DMA) and phenylarsonate (PhA), were efficiently separated by CE in 8 min with an 1.5 mM fluorescein solution at pH 9.8. Fluorescein also functioned as a background fluorophore for the indirect detection of these nonfluorescent arsenic species. Linearity (r greater than or equal to 0.996) of more than two orders of magnitude was generally obtained. The relative standard deviation (RSD) values were in the ranges 0.4-0.7% and 2.2-8.2% for migration times and peak areas, respectively. The concentration limits of detection (CLODs) for the arsenic compounds studied were between 0.04 and 0.16 mu g/mL (as arsenic). The detection sensitivity was generally dependent upon the transfer ratio (TR, defined as the number of moles of fluorescein ions displaced by one mole of analyte ions) of each arsenic species. The applicability of the method for the analysis of ground water was examined.