Capillary electrophoretic determination of As(V) and As(III) based on the formation of a Keggin-type [AsMo12O40]3- complex

A novel capillary electrophoretic (CE) method was developed for the sensitive determination of As(V). In a 1 x 10(-2) M (M = mol/dm(3)) Mo(Vl)-5 x 10(-2) M HClO4-70% (v/v) CH3CN system, a trace amount of As(V) readily formed a mixture of alpha- and beta-[AsMo12O40](3-) complexes. Since the electropherogram showed a sharp peak due to the migration of both complexes, the pre-column complex-formation reaction was applied to the sensitive CE determination of As(V) with direct UV detection at 220 nm. The peak area depended linearly on the concentration of As(V) in the range of 5 x 10(-5) to 5 x 10(-7) M, with a detection limit of 1 x 10(-7) M (signal-to-noise ratio = 5). In a mixture of As(V) and As(III), As(III) could be determined after oxidation to As(V) with H2O2; the As(III) content was estimated by subtracting the As(V) concentration before oxidation from the total arsenic concentration. Interferences from foreign ions were also discussed.