Speciation of mercury in fish samples by flow injection catalytic cold vapour atomic absorption spectrometry

A rapid flow injection catalytic cold vapour atomic absorption spectrometric (FI-CCV-AAS) method is described for speciation and determination of mercury in biological samples. Varying concentrations of NaBH4 were employed for mercury vapour generation from inorganic and mixture of inorganic and organic (total) Hg. The presence of Fe3+, Cu2+ and thiourea had catalytic effect on mercury vapour generation from methylmercury (MeHg) and, when together, Cu2+ and thiourea had synergistic catalytic effect on the vapour generation. Of the two metal ions, Fe3+ gave the best sensitivity enhancement, achieving the same sensitivity for MeHg and inorganic Hg2+. Due to similarity of resulting sensitivity, Hg2+ was used successfully as a primary standard for quantification of inorganic and total Hg. The catalysis was homogeneous in nature, and it was assumed that the breaking of the CHg bond was facilitated by the delocalization of the 5d electron pairs in Hg atom. The extraction of MeHg and inorganic mercury (In-Hg) in fish samples were achieved quantitatively with hydrochloric acid in the presence of thiourea and determined by FI-CCV-AAS. The application of the method to the quantification of mercury species in a fish liver reference material DOLT-4 gave 91.5% and 102.3% recoveries for total and methyl mercury, respectively. The use of flow injection enabled rapid analysis with a sample throughput of 180 h−1.

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► Successful speciation of inorganic and organic Hg with Fe3+, Cu2+ and thiourea as catalysts.
► Best sensitivity enhancement and similar sensitivity for MeHg and Hg2+ with Fe3+.
► Successful use of Hg2+ as the primary standard for quantification of inorganic and total-Hg.
► Quantitative extraction of Hg and MeHg with 2 M HCl which contained thiourea.
► Integration with FIA for rapid analysis with a sample throughput of 180 h−1.