Cold vapour atomic fluorescence studies on the behaviour of mercury(II) and mercury(II)-thiol complexes. An alternative route for characterization of –SH binding groups

Abstract

The behaviour of Hg ^II and Hg ^II -thiol complexes (RSH=L-cysteine, DL-penicillamine, propane-2-thiol, glutathione, thiosalicylic acid) following their reduction with alkaline sodium tetrahydroborate to give Hg ⁰ has been studied by using a continuous flow reaction system coupled with atomic fluorescence spectrometric (AFS) detection. The quantitative reduction of Hg ^II to Hg ⁰ takes place with a specific amount of sodium tetrahydroborate according to the stoichiometric reaction of mercury with alkaline NaBH ₄ . The complete reduction of Hg ^II -thiol complexes to Hg ⁰ requires a molar excess of NaBH ₄ of up to six orders of magnitude, depending on the type of complex. Under an appropriate excess of reductant, Hg ^II and its thiol complexes are not distinguishable giving the same AF molar response. The method allows the discrimination of Hg ^II from Hg ^II -thiol complexes without any preliminary separation. Applications to the indirect titration of thiols and to the determination of the number of accessible }}n1SH groups in pure ovalbumin samples are reported.