Qualitative and quantitative 1 H NMR spectroscopy for determination of divalent metal cation concentration in model salt solutions, food supplements, and pharmaceutical products by using EDTA as chelating agent.

Abstract

This paper introduces an 1 H NMR method to identify individual divalent metal cations Be2+ , Mg2+ , Ca2+ , Sr2+ , Zn2+ , Cd2+ , Hg2+ , Sn2+ , and Pb2+ in aqueous salt solutions through their unique signal shift and coupling after complexation with the salt of ethylenediaminetetraacetic acid (EDTA). Furthermore, quantitative determination applied for the divalent metal cations Ca2+ , Mg2+ , Hg2+ , Sn2+ , Pb2+ , and Zn2+ (limit of quantification: 5-22 μg/ml) can be achieved using an excess of EDTA with aqueous model salt solutions. An internal standard is not required because a known excess of EDTA is added and the remaining free EDTA can be used to recalculate the quantity of chelated metal cations. The utility of the method is demonstrated for the analysis of divalent cations in some food supplements and in pharmaceutical products.