Assay of the synthetic estrogen fosfestrol in pharmaceutical formulations using capillary electrophoresis

This study reports - for the first time - a capillary electrophoretic method for the determination of fosfestrol, a synthetic estrogen used in the treatment of metastatic prostate cancer. The effects of the carrier ion concentration, injected volume and applied voltage were studied and optimized. A 10 mM sodium tetraborate solution was selected as the carrier electrolyte solution, while the sample was injected hydrodynamically by applying a 20 mmHg vacuum for 1 s. The driving voltage was 30 kV and the absorbance of the analyte (peak height) was monitored at 240 nm. Under the above-mentioned conditions, the migration time of fosfestrol was 6.6 min. Linearity was achieved in the analyte range 3-150 mg L−1 with the detection limit being 1 mg L−1. The proposed method is adequately precise (sr = 2.8% at 100 mg L−1 fosfestrol, n = 10) without the use of an internal standard and was applied to the determination of fosfestrol in a pharmaceutical formulation. The results obtained by the proposed method were in good agreement with those derived from the USP reference method.