Effect of Ca2+ on the 1H NMR chemical shift of the methyl signal of oversulphated chondroitin sulphate, a contaminant in heparin.

The chemical shift of the methyl signal of oversulphated chondroitin sulphate (OSCS) is dependent on the type and concentration of the counterion. When OSCS is present as a contaminant in heparin sodium, the reported methyl 1H chemical shift is 2.15 +/- 0.02 ppm. In this report, a value of 2.18 +/- 0.01 ppm is reported for the OSCS in the presence of Ca2+. The chemical shift of the methyl signal of pure OSCS varies linearly from 2.13 ppm to 2.18 ppm with increasing amounts of Ca2+, until reaching the saturation point of four Ca2+ ions per OSCS disaccharide unit, which contains four sulphate groups (a 1:1 ratio between sulphate groups and Ca2+). This Ca2+ effect can be used for OSCS identification as well as to facilitate quantification.