Determination of EDTA in vancomycin by liquid chromatography with absorbance ratioing for peak identification.

An LC method is described for the determination of EDTA in vancomycin formulations. EDTA is complexed with iron and the Fe(EDTA)- complex is separated from vancomycin components on a reversed-phase column using an ion pair mobile phase. Quantitation is achieved using UV detection, with absorbance ratioing employed to discriminate between the analyte and vancomycin-related compounds. The complexity of the sample matrix and the trace levels of EDTA that are of interest dictate unique development considerations. This method offers good specificity and precision over the range 20-300 ppm EDTA in vancomycin formulations, while maintaining a degree of simplicity. Wavelength selection is optimized to demonstrate the potential application of absorbance ratioing to trace determinations. This method has been effectively applied to vancomycin formulations containing a wide range of chemical impurities and is not affected by vancomycin degradation products.