Use of a new enrichment nanosorbent for speciation of mercury by FI-CV-ICP-MS

Abstract

A new enrichment nanosorbent based on mesoporous silica functionalized with 1,5-bis(2-pyridyl) methylene thiocarbohydrazide was synthesized and characterized. From the study of its adsorption capacity toward metal ions, it was observed that Hg²⁺ is one of the elements with higher adsorption capacity on the nanosorbent, 173.1 μmol g⁻¹ at pH 5. Thus, a flow injection solid phase extraction and cold vapor generation method for its determination and speciation based on the use of this new chelating nanosorbent was optimized. The method developed has been shown to be useful for the automatic pre-concentration and sequential determination of mercury and methylmercury in environmental and biological samples. The system was based on chelating retention of the analytes on a mini-column filled with the new nanosorbent and their sequential elution by using two different eluents, 0.2% HCl for CH₃Hg⁺ and 0.1% thiourea in 0.5% HCl for Hg²⁺. The determination was performed using inductively coupled plasma mass spectrometry. Under the optimum conditions and 120 s preconcentration time, the enrichment factors were 4.7 and 11.0, the detection limits (3σ) were 0.002 and 0.004 μg L⁻¹, the determination limits (10σ) were 0.011 and 0.024 μg L⁻¹, and the precisions (calculated for 10 replicate determinations at a 2 μg L⁻¹ standard of both species) were 2.8 and 2.6% (RSD); for CH₃Hg⁺ and Hg²⁺, respectively. Linear calibration graphs were obtained for both species from the determination limits to at least 70 μg L⁻¹. For the quality control of the analytical performance and the validation of the newly developed method, the analyses of two certified samples, LGC 6016 estuarine water and SRM 2976 mussel tissue, were performed. The results showed good agreement with the certified values. Also the method was successfully applied to the speciation of mercury in sea-water samples collected in the Málaga Bay.