Determination of the Concentrations of Metal Cations in Aqueous Solutions Using Proton NMR Spectral Area Integration of the EDTA Complexes

Abstract

This paper introduces an alternative method to determine the concentrations of metal cations in aqueous solutions, using area integration of proton NMR spectra of EDTA (the disodium salt of ethylenediaminetetraacetic acid) metal complexes. Using this method, a certain volume of unknown metal cation solution is added to an excess amount of standard EDTA solution, and the ratio of the remaining free EDTA and the EDTA–metal complex in the solution can be calculated from the integration areas of the proton NMR spectra. Unlike the conventional complexometric titration, where indicators need to be used to determine the endpoint, this NMR method aims to provide a simple method to eliminate the need for using indicators. This method, when EDTA is used as the standard, is valid for determining the concentrations of nonparamagnetic transition and rare earth metal cations, and for the concentrations of group IIIA and IVA metal cations.