Effect of pH on Determination of Various Arsenic Species in Water by HPLC-ICP-MS

BACKGROUND: Previous studies have focused on the effect of pH on separability, choosing an optimal pH by comparing the degree of separation in the determination of different arsenic species by high-performance liquid chromatography-inductively coupled plasma-mass spectrometry(HPLC-ICP-MS).OBJECTIVES: To determine an effective analysis program by comparing the separation, sensitivity and analysis coat at different pH. METHODS: Different species of arsenic compounds were determined by HPLC-ICP-MS, using 30 mmol/L ammonium bicarbonate solution as the eluent. The retention time and peak strength of arsenic compounds were monitored when the pH of the eluent changed between 6.0 and 9.7.RESULTS: In the pH ranges of 6.0-7.5 and 9.5-9.7, the chromatographic peaks of the arsenic compounds were well separated. When the pH value was 8.0-9.0, the peak order of As(Ⅲ) and DMA was exchanged as the pH value increased. When the pH was weakly acidic, the sensitivity of arsenic compounds was higher. When pH was alkaline, the analysis period became shorter and suitable for rapid analysis. About 70% of arsenic compounds in the alkaline eluent combined more strongly to the column and were retained in the column, shortening the life of the column. Acidic eluent was suitable for sample analysis at ultra-low concentrations(e.g.≤10μg/L).CONCLUSIONS: The effect of pH of eluent plays a crucial role in the determination of arsenic species by affecting the binding ability of arsenic compounds to chromatographic column. The acidic eluent has a great advantage in sensitivity. The alkaline eluent has obvious advantages of time and operation cost, but it is necessary to pay attention to the maintenance of the chromatographic column.