Evaluation of two flow injection systems for mercury speciation analysis in fish tissue samples by slurry sampling cold vapor atomic absorption spectrometry

Abstract

Two simple flow injection (FI) systems were used for mercury speciation analysis in slurried fish tissue samples by cold vapor-atomic absorption spectrometry (CV-AAS). The solid samples were first suspended in hydrochloric acid containing Triton X-100 as dispersing agent, and then the slurries were injected in an acid carrier stream, which was either sequentially mixed with sulfuric acid, potassium persulfate oxidizing agent and stannous chloride reducing agent streams or merged with sodium borohydride reducing agent stream. Mercury speciation analysis was carried out as function of the oxidation coil temperature or sodium borohydride concentration, respectively. The detection limit of the method was 57 and 67 ng g⁻¹, referred to dry weight, using the FI system with on-line oxidation for inorganic mercury and total mercury determination, respectively. Nevertheless, the FI system without on-line oxidation resulted in being simpler, faster and more sensitive for inorganic mercury and total mercury determination. Furthermore, the last system permitted the separate determination of methylmercury and inorganic mercury by selecting an adequate hydrochloric acid concentration in the suspension medium and the suitable sodium borohydride reducing agent. The detection limit of the method was 4.04, 0.977 and 11.0 ng g⁻¹, referred to dry weight, for total mercury, inorganic mercury and methylmercury determination, respectively. Both FI methodologies were validated using two fish tissue certified reference materials, NRC DOLT-2 and NRC DORM-2, obtaining results in good agreement with the certified values, and were applied to the analysis of two real mussel tissue samples.