Quantitation of Doretinel in a Topical Gel Using High Performance Liquid Chromatography with Solid Phase Extraction Sample Clean up

Abstract

A stability-indicating method based on high performance liquid chromatography has been developed for the quantitation of doretinel, a new retinoid, at sub-ppm levels in an alcohol gel formulation. A high molecular weight polymer used as a thickening agent in the formulation is removed by solid phase extraction on a C₁₈ column to permit large injection volumes. Samples are assayed on a reversed-phase column packed with 5 micron Spherisorb ODS-II and a mobile phase containing 50% methanol and 10% tetrahydrofuran in a 0.025M potassium phosphate solution. Separations are obtained under ambient conditions with an eluant flow rate of 1.5 mL/min. Placebo interferences are minimized by choosing 300 nm as the detection wavelength. Quantitation is by external standard. Linearity over a wide concentration range is observed. Relative standard deviations for precision and accuracy are less than 3%. Average recovery was 98.4% of theoretical: regression analysis of the data yielded a recovery of 100%.