Evaluation of the gas-liquid separation efficiency of a tubular membrane and determination of arsenic species in groundwater by liquid chromatography coupled with hydride generation atomic absorption spectrometry

An experimental approach for evaluating the hydride separation efficiency of a tubular microporous poly(tetrafluoroethylene) (PTFE) membrane by flow injection hydride generation atomic absorption spectrometry (HGAAS) is described. A method is also proposed for determining arsenic species in groundwater by coupling ion-pair chromatography (IPC) with HGAAS. The evaluation was undertaken with a combined gas-liquid separator (GLS), consisting of a tubular PTFE membrane and a conventional U-shaped glass device. Two important controlling variables, viz., the length of the microporous PTFE tubing and the ratio of the tubing id to the wall thickness, were investigated. The results showed that the absolute separation efficiency of the PTFE membrane can be effectively evaluated with the combined GLS. In addition, arsenic speciation in groundwater was also investigated by IPC-HGAAS. The chromatographic separation of arsenic species with this analytical system was examined in terms of the effects of pH and concentration of eluent. The absolute detection limits achieved with a 100 μl injection can be as low as 0.07, 0.11, 0.12 and 0.30 ng for arsenite (As^III), dimethylarsinic acid, monomethylarsonic acid and arsenate (As^V), respectively. A commercially available standard (NIST SRM 1643b Trace Elements in Water) and the spike additions method were used to confirm the analytical reliability of the method. The proposed method has already been routinely applied to the speciation of arsenic in groundwater samples.