High Performance Liquid Chromatographic Method for the Assay of Undecylenic Acid and Undecylenates in Pharmaceutical Products After Conversion to 4′-Nitrophenacyl Esters

A high performance liquid chromatographic (HPLC) method with spectrophotometric detection is presented for the assay of undecylenic acid, undecylenates (calcium, zinc), and the combination undecylenic acid-zinc undecylenate in commercial antifungal products. To enhance detection, an acetone solution of the sample preparation and sodium octanoate, the internal standard, was derivatized with 4′-nitrophenacyl bromide in the presence of triethylamine at 50°C for 30 min. An aliquot of the reaction mixture was directly analyzed on a Microsorb-MV C8 column, with methanol-acetonitrile-water (50:30:20) as the mobile phase, and detection at 265 nm. At a flow rate of 1.6 mL/min, baseline resolution of the mixture of 4′-nitrophenacyl esters was attained in less than 7 minutes. Detector responses were linearly related to concentrations of reacted undecylenic acid, or its equivalent in an undecylenate, in the range 12.5–300 μg. The recovery of undecylenic acid or an undecylenate from spiked commercial products...