Chromatographic ion-exchange simultaneous separation of arsenic and selenium species with inductively coupled plasma-mass spectrometry on-line detection

The high-performance liquid chromatographic (HPLC) simultaneous separation of arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, selenite, and selenate is studied. The dependence of the retention times of these species on the pH of the mobile phase and on the concentration and chemical composition of buffer solutions (acetate, carbonate, and phosphate) is investigated using a Merck Polyspher IC AN2 and a Hamilton PRP-X100 anion exchange column. With a flame atomic absorption spectrometric detector (FAAS) and arsenic or selenium concentrations of at least 100 mg/L, the best simultaneous separation of these species is achieved on the PRP-X100 column using 0.015M ammonium phosphate buffer at pH 8.5, a 1-mL/min flow rate, and a 20-min analysis time. In a second study, these separation conditions are optimized by using an inductively coupled plasma-mass spectrometric (ICP-MS) detector. The use of a 12.5mM ammonium phosphate buffer adjusted to pH 8.5 with ammonia and a flow rate of 1.5 mL/min is found to be optimal for HPLC-ICP-MS studies with the PRP-X100 column. The analysis time is about 16 min; absolute detection limits are estimated in the range of 11-21 pg for arsenic species and 200 and 417 pg for SeIV and SeVI, respectively. Reproducibility ranges from 2.1 to 3.2%, and the linearity is verified in the 0-200-ng/mL range.