An amperometric method for the determination of trace mercury(II) by formation of complexes with L-tyrosine

A selective and sensitive amperometric method of analysis has been developed for detennination of the trace amounts of mercury in waters at a platinum electrode based on the effect of the presence of mercury ions on the current due to oxidation of L-tyrosine. A decrease of signal was observed due to the formation of a complex of tyrosine with the Hg(II) ion adsorbed on the electrode surface. Several parameters were varied, such as applied potential, pH and concentration of tyrosine. The calibration plot was linear in the range from 0.02 to 3 mumol l(-1) Hg(II) with r = 0.997 and the detection limit (3sigma) was 0.014 mumol l(-1); the relative standard deviation was 2.2%. The study of interferences from other metal ions revealed a good selectivity of this method towards mercury(II). The stoichiometry of the mercury-tyrosine complex was determined to be 1:2 and the formation constant 627 +/- 19. Formation of complexes with mercury ions was also demonstrated with several catechol compounds and other amino acids. The method was applied to the analysis of contaminated waters. (C) 2002 Elsevier Science B.V All rights reserved.