Analysis of arsenic compounds by capillary electrophoresis using indirect UV and mass spectrometric detections

CE with indirect UV and mass-spectrometric detection was used for the simultaneous determination of arsenic acid (As(V)), arsenous acid (As(Ill)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA(+)), arsenobetaine (AB), and arsenocholine (AC). In the CE-indirect UV analysis, a baseline separation of arsenic species was successfully achieved by using a basic background solution (BGS) for anions and an acidic BGS for cations, respectively. The LOD values in CE-indirect UV for the individual analytes were 7.8, 12.5, 7.8, 12.5, 62.5, 125, 250, and 62.5 ppm, respectively. To achieve sensitive and selective analysis, CE coupled with ESI-MS was applied to the determination of arsenic compounds. The organic arsenic species were successfully separated with a higher sensitivity by CE-MS using the acidic BGS. The LODs in CE-MS for MMA, DMA, TMAO, TMA(+), AB, and AC were 1.0, 0.1, 0.01, 0.1, 0.01, and 0.01 ppm, respectively. In contrast, the analysis of inorganic arsenic species (As(V) and As(Ill)) resulted in a lower detectability in CE-MS compared to that obtained with the CE-indirect UV analysis. However, the speciation of eight arsenics by CE-MS was successfully achieved in a single run by switching the ESI polarity during MS detection.