The effect of the sample matrix type (water and aqueous solutions containing phosphate buffer, 3-[cyclohexylamino]-1-propanesulfonic acid [CAPS], and sodium chloride solutions) on the migration behavior and peak parameters of As(III), As(V), and dimethylarsinate was studied. CAPS is found to be the most effective additive for As(III) peak amplification. The reasons for additive influence are discussed. The pH of the carrier electrolyte has been optimized with respect to As(III) peak height and shift of the peak position in electropherograms from the position of the sample matrix plug. Under optimal conditions, a peak efficiency expressed as the number of theoretical plates per meter (N) of 50,460 and a detection limit of 0.05 mg L-1 for As(III) were achieved.