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Within the elements that are toxic for humans and the environment, mercury is a well-known pollutant due to the high toxicity of its species. The toxicity of metals and their bioavailability depend on the chemical form of the metals. All Hg forms are toxic, with the organic species being in most cases more dangerous than the inorganic ones. Bioaccumulation occurs in most cases of human exposure. Seafood is responsible for the highest source of Hg, especially methylmercury (MeHg+). Thus, an accurate analytical method for Hg speciation in seafood is required to assess the real toxicity of samples [1, 2].
This work reports the method development for the simultaneous determination of methylmercury (MeHg+) and inorganic mercury (iHg) species in seafood samples. The study focused on the extraction and quantification of MeHg+ (the most toxic species) by liquid chromatography coupled to on-line UV irradiation and cold vapour atomic fluorescence spectroscopy (LC-UV-HG-AFS), using HCl 4 mol L-1 as the extractant agent.
Accuracy of the method has been verified by analysing three certified reference materials and different spiked samples. The values found for total Hg and MeHg+ for the CRMs did not differ significantly from certified values at a 95% confidence level, and recoveries between 85% and 97% for MeHg+, based on spikes, were achieved. The detection limits (LODs) obtained were 0.001 mg Hg kg-1 for total mercury, 0.0003 mg Hg kg-1 for MeHg+ and 0.0004 mg Hg kg-1 for iHg. The quantification limits (LOQs) established were 0.003 mg Hg kg-1 for total mercury, 0.0010 mg Hg kg-1 for MeHg+ and 0.0012 mg Hg kg-1 for iHg. Precision for each mercury species was established, being ≤ 12 % in terms of RSD in all cases.
Finally, the developed method was applied to 24 seafood samples from different origins and total mercury contents. The concentrations for Total Hg, MeHg+ and iHg ranged from 0.07–2.33, 0.003–2.23 and 0.006–0.085 mg Hg kg-1, respectively. The established analytical method allows obtaining results for mercury speciation in less than one hour including both, sample pretreatment and measuring step.