Plasma-mediated vapor generation of mercury species in a dielectric barrier discharge: Direct analysis in a single drop by atomic absorption spectrometry

Abstract

A plasma-mediated vapor generation (PMVG) by a dielectric barrier discharge (DBD) from a single sample drop of inorganic mercury and methylmercury was investigated and optimized employing for the first time atomic absorption spectrometry (AAS) as a detector. A volume discharge DBD reactor was fabricated together with an inexpensive (<250 USD), but highly flexible laboratory made high voltage power supply. Experimental parameters affecting both the PMVG and subsequent AAS detection steps were optimized. Moreover, the efficiency of PMVG of both species was quantified by two independent approaches: conventional chemical vapor generation (CVG) and the amalgamation technique. Under the optimum PMVG settings, the high voltage power supply was operated at 38 kV, 23 W, 40 kHz and 60% duty cycle, while the DBD reactor was supplied by 150 mL min−1 He discharge gas. Sample volume was optimized to 2 μL. The AAS detection was performed using a quartz tube atomizer kept at ambient temperature. Conversion of both mercury species, Hg2+ and MeHg+, to mercury free atoms (Hg0) inside the DBD reactor has been unequivocally proven. The PMVG efficiency investigated by the two independent approaches was quantified to 87% ± 8% for Hg2+ and 91% ± 10% for MeHg+, respectively. Both mercury species yielded similar sensitivity and limit of detection (LOD) in PMVG-AAS, reaching 0.12 s ng−1 Hg and 100 μg L−1 Hg (200 pg absolute), respectively. Although the generation efficiency as well as the sensitivity reached for both mercury species are comparable between the CVG and PMVG approaches, PMVG reaches significantly worse LODs due to the fact the sample volume is 250-times lower compared to CVG.