Determination of oxalate in pharmaceutical matrices by indirect photometric chromatography

An indirect photometric ion chromatography method is developed for the quantitation of oxalate in typical pharmaceutical matrices. The column/mobile phase conditions used represent a trade off between resolving power and sensitivity and results in an assay with a total analysis time of less than 9 minutes. Method response is linear between concentrations of 10 to 80 ppm oxalate. The limit of quantitation is roughly 5 ppm. Precision in the range of 30 to 80 ppm is better than 1.0% RSD of replicate injections, and the accuracy in a variety of matrices is 100 +/- 2%. The method is quite rugged and meets rigorous suitability requirements even after 500 injections. Although the assay can be used to quantitate citrate as well, the retention time is relatively long (20 minutes) and sensitivity is limited due to the broadness of the peak.