Determination of methylmercury by solid-phase microextraction inductively coupled plasma mass spectrometry: a new sample introduction method for volatile metal species

Direct coupling of solid-phase microextraction (SPME) with inductively coupled plasma mass spectrometry (ICP-MS) is described for methylmercury speciation. A thermal desorption interface, consisting of a heated, glass-lined splitless-type GC injector, was placed directly at the base of the torch to minimize the length of transfer line. This arrangement provides for fast desorption and high sample introduction efficiency. Direct liquid immersion and headspace extraction of methylmercury was studied, including the effect of temperature and time on the extraction efficiency. For clean solutions, immersion sampling SPME provided good sensitivity that was linear over two orders of magnitude whereas headspace sampling showed 15% lower sensitivity, but a linear range of more than three orders of magnitude. The detection limit for headspace methylmercury sampling was 0.2 ng ml(-1). Calibration by the method of additions using direct extraction revealed a severe matrix effect with biological tissue samples, diminishing the methylmercury response 70-fold, whereas that obtained by headspace extraction was statistically indistinguishable from signals generated using matrix free standards. Analytical results showed good agreement between certified and measured values for analysis of NRCC DORM-2, (Dogfish muscle) and DOLT-2 (Dogfish liver) reference materials.