Mercury Speciation by Hydride Generation Atomic Absorption Spectrometry after Ion Exchange Separation in a FIA System (FIA-IE-HG-AAS)

摘要

Ion exchange is presented as a simple, non-expensive technique for the effective separation of inorganic mercury (Hg~(2+)) and methylmercury (MeHg~+) in hydrochloric media. Preliminary experiments using Pasteur pipettes packed with different resins were carried out in batch mode to define the best anionic exchanger and elution agent in terms of separation and elution efficiency. An Omnifit microcolumn packed with the selected resin was then implemented in a commercial FIA manifold to measure total mercury by cold vapor atomic absorption spectrometry. The geometry of the microcolumn (length and diameter) was optimised to get quantitative retention of Hg~(2+) and simultaneous maximum sensitivity in the analysis of MeHg~+. The concentration of the elution agent (cysteine) was then also investigated to optimise the sensitivity in the Hg~(2+) analysis. Finally, the weakly anionic exchanger Dowex M-41, a 10 cm lenght and 6.6 mm i. d. microcolumn and a 0.1 mol-dm~(-3) cysteine solution were selected as the best conditions to perform the analysis. The FIA system proposed allows the consecutive analysis of MeHg~+ and Hg~(2+) in a single injection of sample. Analysis of estuarine water samples spiked with both analytes was carried out following the described methodology.