Voltammetric Analysis of Phytochelatin Complexation in Ternary Metal Mixtures Supported by Multivariate Analysis and ESI‐MS

The competitive binding of Cu 2+ , Cd 2+ and Pb 2+ in ternary mixtures by the phytochelatins PC 2 and PC 5 (PC n ; (γGlu‐Cys) n ‐Gly, n =2 and 5) are examined by voltammetry, which allows one to follow the displacements of the voltammetric signals induced by the competitive binding among the metal ions towards PC 2 or PC 5 complexation, and direct injection positive‐mode Electrospray Ionization Mass Spectrometry (ESI‐MS), in order to obtain the stoichiometries of the complexes. Voltammetric data are analyzed by Gaussian Peak Adjustment (GPA), which is a recently developed multivariate analysis method for nonlinear electrochemical data. Different complexes have been detected or deduced their presence, depending on the experimental conditions. Ternary complexes CuCdPC n and CdPbPC n were detected for both PC 2 and PC 5 , while the ternary CuPbPC n complex was only detected for PC 2 . Some of the complexes have been only detected by ESI‐MS because in some cases voltammetry data could not be totally resolved, even by using GPA. The quaternary CdPbCuPC n complex has been detected for PC 5 , but for PC 2 data are not so conclusive. In summary, the signal evolution for mixed CdCuPC n complexes is quite different. These observations could be a reflection of an antagonistic effect for the case of PC 2 and a synergetic one for PC 5 .