Search

Anion-exchange chromatography (Hamilton, PRP-X100) with inductively coupled plasma mass spectrometry (ICP-MS) is commonly used for the speciation of arsenic in environmental and biological samples. However, retentions for As species are frequently different because of the use of widely different mobile phases. In addition, chloride in matrices interferes with arsenic determination. In this study, we systematically investigated various mobile phases based on ammonium salts affecting arsenic retention to eliminate chloride interference chromatographically. Hence, various mobile phases based on ammonium salts, including NH4H2PO4, NH4HPO4, NH4Ac, NH4HCO3 and NH4NO3, were examined for reasonable resolution and to separate chloride from arsenic species. The best result was obtained with a mobile phase containing 30 mM NH4H2PO4 at pH 5.6, where the separation of arsenic species, including arsenite [As(III)], arsenate [As(V)], dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA)], was achieved within 9 minutes with reasonable resolution and free of chloride interference at its high level (500 mg L− 1). The detection limits for the arsenic species were in the range of 0.1–0.3 μg L− 1 with a direct injection of sample without removing matrix. Finally, the proposed method was used for the determination of arsenic species in contaminated soil and plant tissues.

The use of capillary electrophoresis (CE) and UV detection for the determination of metal speciation is based on the standards via matching migration time. Consequently, it requires that the metal species are stable during electrophoresis. Migration time of the metal species is dependent on the electrolyte composition. However, the stability for such metal complexes is also dependent on electrolyte composition and electrolyte-specific stability is not always well known. In this paper, the stability of iron (Fe) polycarboxylate complex formation was determined using electrospray ionization mass spectrometry (ESI-MS). Mass spectra indicates that Fe[DTPA] 2− , Fe[EDTA] − , Fe[HEDTA] and Fe[NTA] were present in solution but the mass spectrum for Fe[NTA] was found to be weak. An electrolyte containing 25 mM NaH 2 PO 4 and 0.25 mM tetradecyltrimethylammonium bromide (TTAB) at pH 6.0 was used to successfully separate Fe[DTPA] 2− , Fe[EDTA] 1− and Fe[HEDTA]. The instability of Fe[NTA] meant it was not observed due to its instability during electrophoresis. To improve UV detection limits sample stacking techniques, such as large volume sample stacking (LVSS) without polarity switching and filed-amplified sample injection (FASI), were investigated. The results show that less than 0.01 μM detection limits for the Fe complexes were obtained using FASI. The calibration plots were linear from 0.05–3.0 with good reproducibility (peak area: 6.5–8.1%) when a water plug was used. Finally, the proposed method was demonstrated for the determination of trace Fe complexes in river waters.