THE ION-CHROMATOGRAPHIC BEHAVIOR OF ARSENITE, ARSENATE, METHYLARSONIC ACID AND DIMETHYLARSINIC ACID ON THE HAMILTON PRP-X100 ANION-EXCHANGE COLUMN

The HPLC separation of arsenite, arsenate, methylarsonic acid and dimethylarsinic acid has been studied in the past but not in a systematic manner. The dependence of the retention times of these arsenic compounds on the PH of the mobile phase, on the concentration and the chemical composition of buffer solutions (phosphate, acetate, potassium hydrogen phthalate) and on the presence of sodium sulfate or nickel sulfate in the mobile phase was investigated using a Hamilton PRP-X100 anion-exchange column. With a flame atomic absorption detector and arsenic concentrations of at least 10 mg dm-3 all investigated mobile phases will separate the four arsenic compounds at appropriate pH values in the range 4-8. The shortest analysis time (approximately 3 min) was achieved with a 0.006 mol dm-3 potassium hydrogen phthalate mobile phase at pH 4, the longest (approximately 10 min) with 0.006 mol dm-3 sodium sulfate at pH 5.9 at a flow rate of 1.5 cm3 min-1. With a graphite furnace atomic absorption detector at the required, much lower, flow rate of approximately 0.2 cm3 min-1 acceptable separations were achievable only with the pH 6 phosphate buffer (0.03 mol dm-3) and the nickel sulfate solution (0.005 mol dm-3) as the mobile phase. To become detectable approximately 100 ng arsenic from each arsenic compound (100 mul injection) must be chromatographed with the phosphate buffer, and approximately 10 ng with the nickel sulfate solution.