Multivariate optimization of photochemical vapor generation for direct determination of arsenic in seawater by inductively coupled plasma mass spectrometry

Photochemical vapor generation (PVG) sample introduction coupled to inductively coupled plasma mass spectrometry (ICPMS) is described for the determination of As in seawater. A Plackett–Burman design (PBD) and central composite design (CCD) were employed to evaluate the significance of experimental variables relevant to the optimization of PVG-ICPMS detection. The impact of the saline matrix on the suppression of analyte signal was eliminated by use of a mixture of 20% (v/v) formic and 20% acetic acid (v/v) as the photochemical reductants. Optimized conditions yielded equivalent PVG generation efficiencies for As(III), As(V), monomethylarsonic acids (MMAs) and dimethylarsinic acids (DMAs), permitting direct and rapid determination of total arsenic in seawater without any other sample pre-treatment. Quantitation was accomplished using one point gravimetric standard addition along with a spike of ⁸²Se internal standard to compensate for signal drift and fluctuation during analysis. The resulting method detection limit of 3 pg g⁻¹ (3σ) provided a 15-fold improvement over that obtained using direct solution nebulization, and is comparable to that for conventional chemical hydride generation (HG)-ICPMS. Accuracy was demonstrated by analysis of two Certified Reference Materials (NASS-6 and CASS-5 seawater) with satisfying results characterized by precisions of 3.5% and 3.2% RSD for CASS-5 and NASS-6, respectively.