Determination of arsenic species by field amplified injection capillary electrophoresis after modification of the sample solution with methanol Original Research Article

Organic solvent modification is investigated as a simple and effective way to decrease the conductivity of liquid samples containing anionic As species, making them suitable for field amplified sample stacking capillary electrophoresis (CE) measurements with direct UV detection. Experimental variables that influence the procedure, as buffer pH, stacking and running potential, are described for methanol, selected as the optimum sample modifier. The influence of modifying the CE buffer with methanol on the resolution is also discussed. Results of stacking with and without removing the sample matrix from the capillary (with and without polarity switching after the stacking stage) are reported. The optimized method permits the determination of As(III) (arsenite), free As(V) (arsenate), and dimethylarsinate (DMA), in the range from 0.5 to 20 mg/l, with detection limits around 0.3 mg/l. For other As(V) compound of human origin, phenylarsonate (PAA), and p-aminobenzenearsonate (PABA), the power of detection is higher due to their higher extinction coefficients. The linear range extends from 20 to 1000 μg/l, with a detection limit of 11 μg/l (PAA) and 16 μg/l (PABA).