Study of the Behavior of Arsenic in Microwave Plasma Torch-Mass Spectrometry

Based on the coupling of hydride generation (HG) and microwave plasma torch (MPT), a rapid and sensitive method of hydride generation-microwave plasma torch-mass spectrometry (HG-MPT-MS) for arsenic under atmospheric condition was developed. The mass spectral behavior of arsenic under different ionization conditions was investigated. In both positive and negative ion modes, arsenic displayed characteristic mass spectrum peaks, which was significantly different from electrospray ionization (ESI), inductively coupled plasma (ICP) and other common ionization techniques. HG-MPT-MS enabled ionization of analytes at molecular level, and it formed adduct ions with NO₃^-, and even dimers of arsenate ions. Due to the combination of hydride generation and microwave plasma torch, the background noise and the signal intensity of analytes were greatly improved. Therefore, this method was suitable for direct mass spectrometry analysis of trace arsenic in complex samples. In addition, the influence of HCl concentration on the signal intensity, and the regulation of arsine generation behavior by microwave power were studied. Compared with ICP, microwave plasma torch showed more obvious advantages on the analysis of arsenic, such as extremely low power and argon consumption, soft ionization and continuous energy regulation. The total ion chromatography (TIC) and the extracted ion chromatography (EIC) of all analytes displayed good signal stability and peak shape. In addition, arsenic concentration and its signal intensity showed a good linear relationship (R²>0.998) in the concentration range of 1-500 μg/L, and the detection limit was 0.02 μg/L. This method was applied to analysis of a reference water standard and two real water samples of lake water and river water. The results showed that the determined value was in agreement with the certified value for the reference standard. Spiked recoveries of the river water and lake water samples ranged from 95.0% to 105.0% with the relative standard deviation (RSD) of 8.0%-11.0%. On the other hand, the commonly used hydride generation-atomic fluorescence spectrometry (HG-AFS） was also compared with MPT and ICP, which was more economic on power and argon consumption, and had even lower detection limit. However, MPT might have more advantages on simultaneous analysis of multi-elements, such as As, Sb, Bi, Se, Te, Hg and so on. This method was expected to provide a useful tool for sensitive analysis of As and other metalloids from complex matrices.