Simultaneous quantitative speciation of selected toxic elements in water using high performance liquid chromatography coupled to inductively coupled plasma-mass spectrometry (HPLC-ICP-MS)

Abstract

The aim of this study was to conduct multi-elemental speciation of As(III), dimethylarsinic acid (DMA), monomethylarsenic acid (MMA), As(V) and Cr(VI) in water samples using high performance liquid chromatography coupled to inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) in a single analytical run. Chromatographic parameters, spectral interference identification, and elimination and the performance characteristics of the method were successfully optimized for quantification of As(III), DMA, MMA, As(V), Cr(VI) and Cr(III) in water samples. The percentage errors of 6.93–43.2% for identified potential interferences were eliminated by applying the inter-element mathematical correction method. The limit of detection (LOD) and limit of quantification (LOQ) of As species and Cr(VI) were varied from 0.040-0.298 μg L−1 and 0.133–2.98 μg L−1, respectively. The LOD and LOQ of total As, Cr and Pb determined using ICP-MS were ranged from 0.013-0.203 μg L−1 and 0.045–0.675 μg L−1, respectively. The accuracy of the method was confirmed by achieving the percentage recovery of 83.4% for As species, 90.2% for Cr(VI) and 110–118% for total concentrations of As, Cr and Pb using standard reference material for trace elements in water (SRM 1643f). Furthermore, the accuracy of the speciation analysis method was checked using the spiking and recovery studies and yielded percentage recoveries in the range of 78.3–95.4% for the analyte species. The quantities of species determined in water samples were in the range of 0.314–0.402 μg L−1 for As(III), 0.168–0.533 μg L−1 for DMA, 0.226–0.312 μg L−1 for MMA, 0.191–0.459 μg L−1 for As(V), 0.500–3.28 μg L−1 for Cr(VI) and 0.390–12.6 μg L−1 for Cr(III) in high-flow seasonal state of the river. In the low-flow seasonal state, concentrations varied from 0.314-0.391 μg L−1 for As(III), <0.094 μg L−1 for DMA, 0.315–26.7 μg L−1 for MMA, 0.290–0.744 μg L−1 for As(V), 0.426–5.42 μg L−1 for Cr(VI) and 0.424–96.8 μg L−1 Cr(III). Total concentrations of As, Cr and Pb in water samples of high-flow seasonal state ranged from 0.949-1.88 μg L−1, 1.08–14.9 μg L−1 and 0.190–33.8 μg L−1, respectively. In low-flow seasonal state, the total concentrations of As, Cr and Pb in water samples varied from 1.13-26.5 μg L−1, 3.28–97.5 μg L−1 and 0.455–0.610 μg L−1, respectively. The variations between analytes species and total As, Cr and Pb in seasonal states of the river were statistically insignificant (p > 0.05) at a 95% confidence level except for DMA. The nonpoint sources pollution such as atmospheric deposition of dust released from coal mining, power stations, sewage effluents discharge and agricultural activities are presumably the sources of potentially toxic elements in the Mokolo River.