Purity Determination of Alprostadil by Micellar Electrokinetic Chromatography with Signal Enhancement Involving Field‐Amplified Sample Stacking and Extended Path Length Detection

Abstract

Two related procedures based on micellar electrokinetic chromatography (MEKC) were developed and validated for purity determination of alprostadil. Alprostadil is the active ingredient in Caverject DCS, indicated for erectile dysfunction. The techniques of field‐amplified sample stacking and high sensitivity optical cell enhancement were used. For the former, the sample was injected for 20 s under vacuum followed by a sample buffer zone backout at −10 kV for 0.9 min. For the latter, which relies on extended path length detection via a capillary/z‐cell configuration, the sample was injected under vacuum for 5 s with no stacking of the sample zone. All process and degradation impurities were separated from the internal standard and from PGE1 except for 11‐epi‐PGE1, which appears as a shoulder on the front edge of the PGE1 peak. The precision for both techniques meets current validation expectations, generally below ±1%, always below ±2%. Linearity/recovery from 70–120% using reversed polarity electrostacking resulted in a mean recovery of 100.0% with an RSD of 0.81%. For the capillary/z‐cell the mean recovery was 100.9% with an RSD of 1.3%. Results obtained by both MEKC procedures on two lots of alprostadil were comparable to HPLC. There was no statistical difference between means at the 95% confidence interval. Hence, the two variants on MEKC provide an orthogonal means to HPLC for assessing the purity of alprostadil.