Application of a nitrogen microwave-induced plasma mass spectrometer as an element-specific detector for arsenic speciation analysis

Abstract

A high power nitrogen microwave-induced plasma (1.3 kW) mass spectrometer (N2-MIP-MS) was successfully coupled with an HPLC system using a silica-based cation-exchange column. It was examined as an element-specific detector for its applicability to the optimization and determination of seven arsenic compounds [As(V), methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), arsenocholine (AC), trimethylarsine oxide (TMAO) and tetramethylarsonium ion (TMI)]. The system is a promising alternative ion source for mass spectrometry for elemental speciation analysis. The MIP was stable with a pyridine mobile phase for up to 6 h. Replacing the MIP-MS fabricated nebulizer (concentric) and sample input tubing (PTFE) with an ICP-MS (PMS-2000) nebulizer (concentric) and PEEK tubing increased the ion signals for anionic and cationic arsenic compounds by 17–30 and 21–25%, respectively. PEEK tubing additionally increased the separation efficiency for the arsenic compounds. The detection limits of As(V), MA, DMA, AB, TMAO, AC and TMI obtained with the optimized HPLC-N2-MIP-MS system were 0.68, 0.95, 2.01, 0.92, 22.1, 1.31 and 1.75 µg l–1, respectively. The repeatability (RSD for three successive analyses) and reproducibility lRSD for three successive analyses performed on three different days) achieved were 0.7–9.22 and 6.5–11.4%, respectively, for the seven different arsenic compounds. No detectable spectroscopic interference of 40Ar35Cl+ was observed with a high chloride matrix (10 000 mg l–1). The developed HPLC-N2-MIP-MS method was successfully applied to the determination of arsenic compounds, principally AB, in NIES Candidate CRM-18 Freeze-Dried Human Urine (134 ± 6 µg l–1). The results agreed reasonably well with the HPLC-ICP-MS values.