Abstract:
New possibilities in collection of polarographic and potentiometric experimental data in
studies of metal–ligand systems by automated instrumental methods, and subsequent
treatment of the polarographic data, whereby the degree of reversibility of the electrode
processes varies, have been investigated in this work. An automated instrumental set–up
was developed for applications in studies of metal–ligand solution equilibria by
potentiometry and sampled Direct Current Polarography (DCP). The new set–up was
designed based on virtual instrumentation principles whereby several commercially–
available hardware units as well as custom–built electronic components, were interfaced
to a personal computer that was equipped with appropriate hardware and control
programs. The instrumental set–up was tested and validated by studying the protonation
equilibria of the ligand glycine by Glass Electrode Potentiometry (GEP) as well as the
complexation of the ligand glycine with Cd2+ by GEP and DCP. The new set–up provides
increased versatility, accuracy and convenience in obtaining large numbers of
experimental points in solution equilibria studies by DCP and GEP as opposed to the use
of tedious and time–consuming manual methods. Nonlinear curve–fitting procedures,
based on closed–form models that were derived here from suitable theoretical equations
identified from literature, have been investigated in this work for applications in analysis
of DC curves recorded on metal–ligand systems with variation in electrochemical
reversibility. The applicability and limitations of the curve–fitting procedures developed
have been tested in analysis of the DCP data collected on several metal–ligand systems
involving Cd2+, Pb2+, Zn2+ and the ligands glycine and sarcosine, whereby the DCP
studies of these systems exhibited reversible, quasi–reversible or irreversible
electrochemical processes. Information on applicability and limitations of the proposed
methods investigated in this work was derived by comparison of the results obtained from
DCP, using the proposed methods, with either reported literature data and/or results
obtained in this work by the independent analytical technique of GEP, which was
deployed wherever it was found to be applicable to study the metal–ligand systems
considered.
