Ion-exchange liquid chromatographic analysis of bisphosphonates in pharmaceutical preparations

A simple, fast and uniform method has been developed for the quantitative determination of bisphosphonates in the quality control of pharmaceutical preparations. The method is based on ion-exchange liquid chromatography with conductivity detection. Separation is performed on a Waters IC-PAK Anion column using 2 mM nitric acid or 25 mM succinic acid as the mobile phase. Retention of the bisphosphonates can be influenced by pH and the anion concentration of the mobile phase. Sensitivity and selectivity are sufficient for the assay of bisphosphonates in bulk drug and pharmaceutical preparations. Sample preparation comprises dissolution or dilution of the sample in the mobile phase followed, if necessary, by filtration prior to HPLC analysis. Since the method is stability indicating, it is also well suited for shelf-life studies of bisphosphonate pharmaceutical preparations. Validation of the analytical method for the assay of pamidronate injection indicated an intra-day reproducibility of 1.7% (n = 6) and an inter-day reproducibility of 2.7% (n = 6). A linear relationship between response and concentration was found in the concentration range studied from 200 ng to 10 micrograms pamidronate per 20 microliters injected. The lower limit of detection (signal-to-noise ratio = 3) of pamidronate was about 100 ng.