Arsenic speciation in marine certified reference materials
Part 1. Identification of water-soluble arsenic species using multidimensional liquid chromatography combined with inductively coupled plasma, electrospray and electrospray high-field asymmetric waveform ion mobility spectrometry with mass spectrometric detection
Certified reference materials (CRM) of marine origin were characterized for arsenic-containing species. A multidimensional liquid chromatography (LC) protocol consisting of preparative anion-exchange followed by semi-preparative cation-exchange or anion-exchange high-performance liquid chromatography (HPLC) was employed to isolate, purify and identify organoarsenic species. Inductively coupled plasma mass spectrometry (ICP-MS) was employed off-line to monitor the LC effluent (1st dimension) and on-line with HPLC (2nd dimension) for mapping of key fractions. Electrospray mass spectrometry (ES MS) was employed for the analysis of arsenic-containing HPLC fractions and interpretation of collision induced dissociation spectra confirmed species identification. For minor species, whose concentrations approached the limit of detection of ES MS, high-field asymmetric waveform ion mobility spectrometry (FAIMS), a novel technique based on ion mobility spectrometry, was employed. A FAIMS device inserted between the ES source and the MS allows for the separation/focussing of ions in the gas phase and reduction of an interfering matrix. This is the first report of FAIMS being used for trace element speciation in biological tissues. The major species in all the CRMs was found to be arsenobetaine (AsB). Other species identified in the purified CRM extracts by ES MS included trimethylarsoniopropionate (TMAP), dimethylarsinic acid (DMA), monomethylarsinic acid (MMA) and arsenosugar D (As-sug D). Where ES MS was unsuccessful, ES-FAIMS-MS allowed the identification of arsenocholine (AsC+) and tetramethylarsonium ion (TMAs+). Arsenite (AsV) and arsenosugar A (As-sug A) were tentatively identified by retention time matching with standards.