Total determination and direct chemical speciation of Hg in fish by solid sampling GF AAS

Abstract

Simple and rapid analytical procedures for the direct determination of total Hg and for direct chemical speciation of Hg²⁺ and methylmercury (MHg) in fish were proposed after careful optimization of the heating program and the addition of appropriate chemical modifiers by solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). The total determination was done using Ir film and 5 μg Pd + 3 μg Mg solution as permanent and co-injected chemical modifiers, respectively. For direct chemical speciation, 5 μg Pd + 3 μg Mg or 5 μg Pd + 3 μg Mg + 0.5% w/v Triton X-100 solutions were used as co-injected chemical modifiers. The accuracy of both procedures was verified using the certified reference material (CRM) of tuna fish (CE-464), lobster hepatopancreas (TORT-2) and dogfish (DOLT-2). The certified and the found concentrations were statistically concordant (Student's t-test). The total Hg concentration in the tuna fish candidate reference material produced in our laboratory was 2.66 ± 0.15 mg kg⁻¹. In the sample ground in a cryogenic mill, the Hg²⁺ concentrations were 0.553 and 0.559 mg kg⁻¹ and by the difference between the total Hg and Hg²⁺ concentration was obtained the MHg concentration, 5.11 and 4.73 g kg⁻¹, using Pd + Mg and Pd + Mg + Triton respectively. These results reveal a high concentration of the methylated species that it is most toxic Hg species.