COMPLEXATION STOICHIOMETRY DETERMINED BY APPLICATION OF CHEMOMETRICS TO TIME-DOMAIN NUCLEAR-MAGNETIC-RESONANCE SIGNALS

The objective of this study is to demonstrate the feasibility of using multivariate statistical techniques applied to Time Domain - Nuclear Magnetic Resonance (TD-NMR) signals to determine the stoechiometry of complexation reactions. The complex used here is the well known EDTA-m angnese complex. The measurement is based on the change in the interac tions between the paramagnetic manganese cation and the solvent depend ing on whether it is free in solution or chelated with EDTA. Free mang anese significantly increases the relaxation rate of the solvating wat er protons while chelated manganese has a weaker effect. The complexat ion is studied using Job's Continuous Variations Method. The system is analysed in two ways. In a first step R-1 and R-2 relaxation rates ar e calculated by non-linear regression and are shown to be sensitive pa rameters for determining the stoechiometry of the complex. In a second step, rile normalised TD-NMR signals are directly analysed using Prin cipal Components Analysis (PCA) and Evolving Factor Analysis (EFA). Th ese multivariate statistical analyses of the signals are also shown to be good methods for detecting the complexation.