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

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.