Plasma-mediated mercury vapor generation after microwave-induced combustion of fish tissue with detection by atomic absorption spectrometry

Abstract

Mercury determination in fish tissues by high-resolution continuum source atomic absorption spectrometry (HR-CS AAS) was performed using microwave-induced combustion (MIC) for sample preparation, and plasma-mediated vapor generation (PMVG) in a tubular dielectric barrier discharge (DBD) as a sample introduction system. The main goal was to develop a method for Hg determination using very low amount of reagents being at the same time virtually free of interferences. The operational parameters of the PMVG step in the DBD reactor were optimized as follows: 70 mL min⁻¹ Ar as the discharge gas, 20 mm electrode distance, primary voltage at 60 V and 50 μL as digested sample volume (in 0.1 mol L⁻¹ HNO₃ matrix). The effect of HNO₃ concentration on the PMVG efficiency was studied. No differences in signal intensity were observed for HNO₃ concentration up to 0.1 mol L⁻¹, while a signal decrease by 25 % and 40 % was observed when the acid concentration increased to 1 and 5 mol L⁻¹, respectively. Accuracy of the proposed method was evaluated using certified reference material (CRM) of dogfish liver (DOLT-4) and by Hg spikes on the sample prior to MIC. By using 500 mg of sample (or 250 mg of CRM) and 6 mL of 0.5 mol L⁻¹ HNO₃ as absorbing solution in MIC, recoveries of 104 % and 97 % were observed for spikes and CRM values, respectively. A limit of detection of 0.16 μg g⁻¹ Hg (160 pg Hg absolute) was obtained. A comparison of the results for Hg determination in the CRM by PMVG-AAS and chemical cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS) was performed with no significant differences in the results. Finally, an efficient, low-cost and low-volume reagent consumption sample introduction system for Hg determination by AAS was successfully combined with the advantages of MIC and subsequent PMVG by DBD.