Separation of arsenic species by capillary electrophoresis with sample-stacking techniques

A simple capillary zone electrophoresis procedure was developed for the separation of arsenic species (ASO(2)(2-), ASO(4)(2-), and dimethylarsinic acid, DMA). Both counter-electroosmotic and co-electroosmotic (EOF) modes were investigated for the separation of arsenic species with direct UV detection at 185 nm using 20 mmol L-1 sodium phosphate as the electrolyte. The separation selectivity mainly depends on the separation modes and electrolyte pH. Inorganic anions (Cl-, NO2-, NO3- and SO42-) presented in real samples did not interfere with arsenic speciation in either separation mode. To improve the detection limits, sample-stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were investigated for the preconcentration of As species in co-CZE mode. Less than 1 mumol L-1 of detection limits for As species were achieved using FASI. The proposed method was demonstrated for the separation and detection of As species in water.