Measurement of Molecular Species of Arsenic and Tin Using Elemental and Molecular Dual Mode Analysis by Ionspray Mass Spectrometry

Abstract

Ionspray mass spectrometry has been employed for dual mode, molecular and elemental, detection and quantification of tributyltin and arsenobetaine. A selectable degree of ion–solvent declustering and molecular fragmentation in the ion source–mass spectrometer interface region permitted detection of fully intact molecular species, or fragments of the molceular species to any selected degree. Complete dissociation of the molecular species in the interface region enabled detection of the underlying element of interest. Tandem mass spectrometry (MS–MS) was used in the molecular detection mode to increase selectivity of the analysis. Instrumental parameter adjustment permitted dual mode detection for the same sample on subsequent injections. Dual mode detection using FI was performed to determine the tributyltin concentration in the National Research Council of Canada (NRCC) harbour sediment reference material PACS-1. Measured tributyltin concentrations were 1.24±0.04 µg g ^-1 of Sn in the sediment (MS–MS mode) and 1.29±0.04 µg g ^-1 of Sn in sediment (elemental mode), compared with the certified value of 1.27±0.22 µg g ^-1 of Sn in sediment. The dual mode detection system was coupled to two forms of liquid chromatography, cation exchange and ion-pairing, to determine arsenobetaine concentration in the NRCC dogfish muscle reference material DORM-2, as part of the NRCC certification process. Results of the two detection modes with both chromatographic methods were consistent, and yielded a mean arsenobetaine concentration of 16.6±0.6 µg g ^-1 of As in the material. Although the certification process is not complete, this result was consistent with an expected arsenobetaine level slightly higher than previously measured values of 15.7±0.4 µg g ^-1 of As in for DORM-1, the NRCC predecessor reference material to DORM-2. Additionally, an intermediate mode of interface fragmentation coupled with MS–MS enabled the detailed mapping of possible collisionally induced dissociation channels for arsenobetaine.