ProMCC: An all-in-one tool for trace metal complexation studies

Abstract

A new windows-based, user friendly program (ProMCC) for (i) the determination of metal complexation parameters (ligand concentration (L) and conditional stability constants (K′)) and for (ii) theoretical simulation of metal complexometric titration, assuming discrete ligand model, is developed. Although primarily intended for treatment of experimental data obtained either by anodic stripping voltammetry (ASV) or competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV), it could manage titration-type data of other techniques (e.g. ISE, sorption isotherm). Currently, the program is capable to process (fit and/or simulate) titration data up to three discrete ligand classes. Procedure for adjustment of “true” analytical sensitivity incorporated in ProMCC was found to provide reasonably good estimates of sensitivity either for one-ligand or two-ligand system. The particular feature of ProMCC is that it incorporates two complementary fitting methodologies: (1) a non-linear fitting of conventional linearized transformations (e.g. Ružić/Van Den Berg, Langmuir/Gerringa) and (2) a “complete complexation model” — a matrix based optimization of mass balance equations. Comparison test of different non-linear fitting modes and titration types revealed that a slight underestimation of ligand concentration and overestimation of conditional stability constant may occur if titration is performed in logarithmic mode, mainly due to unfavorable noise distribution. An advantage of implemented “complete complexation model” fitting mode is that it allows simultaneous analysis of titrations obtained at multiple detection windows as unified dataset (multi-detection window approach), providing complexation parameters for up to three ligand classes. A new alternative “RAL-approach” in analyzing complexometric titrations obtained at multiple detection windows for copper–salicylaldoxime (Cu–SA) system is suggested. It assumes that the analytical sensitivity is changing along the titration curve respecting the true speciation of Cu–SA in sample. An adapted empirical equation for calculation of relative intensity (RAL) is proposed. Flexibility in adjusting parameters, immediate graphical feedback and visualizations make ProMCC handy for treatment of large set of experimental data, and a tool for research in refinement of the methods of metal complexing capacity determination which is continuously improving.