Electrospray Mass Spectrometry of Arsenic Compounds and Thiol–Arsenic Complexes

Abstract

AbstractThis article reviews the identification and quantification of arsenic species and their complexes using electrospray ionization mass spectrometry (ESI‐MS). Topics covered include accurate mass determination, select ion monitoring (SIM) and multiple reaction monitoring (MRM), isotopic ratios, common fragmentation patterns, transition ratios, wrong‐way‐round ionization, crosstalk, ion interference, and matrix effects. The analytical methods range from direct‐infusion ESI‐MS and tandem mass spectrometry (MS/MS), to the coupling of the ESI‐MS to high‐performance liquid chromatography (HPLC) separation, and finally to combined analysis using HPLC separation with both inductively coupled plasma mass spectrometry (ICP‐MS) and HPLC/ESI‐MS detections. The combination of both ICP‐MS and ESI‐MS is especially powerful, benefiting from the established, robust, and sensitive element‐specific detection of ICP‐MS, and the molecular detection of ESI‐MS. Using the various mass spectrometry (MS) techniques, a variety of biological and environmental samples have been studied, including the urine of humans and animals, food and plants grown on arsenic‐contaminated soil, surface water, and contaminated groundwater. This article also discusses recent studies on the formation of thiol‐arsenic complexes between select arsenic species and thiols such as glutathione (GSH) and metallothionein (MT). The use of ESI‐MS contributes to determining the stoichiometry and binding location, monitoring the reaction in real time, and evaluating binding constants. Information from binding studies has helped the development of improved ESI‐MS methods through derivatization of arsenic species with thiols.