An innovative spectrophotometric method for determination of polidocanol in pharmaceutical ampoules using phase equilibrium measurements

A simple spectrophotometric method was developed for determination of the challenging surface active non-chromophoric pharmaceutical product; polidocanol (PD). The assay principle depends on the ability of PD to form a ternary complex with the tetrahedral cobalt (II)-thiocyanate blue complex, due to the poly(ethylene oxide) group. The hydrophobic chain in PD allows the formed ternary complex to be extracted in the dichloromethane layer, which turns blue after addition of PD and shaking. The absorbance of the extracted ternary complex can be monitored to measure the concentration of PD. The proposed method was found selective and suitable for determination of PD in pharmaceutical dosage forms, with no interference from excipients. The different factors that may affect the method sensitivity were studied, including the type of extractant, the wavelength, the complex concentration, the mixing and the extraction time. The maximum sensitivity was attained when the absorbance was measured at 320 nm using dichloromethane as an extractant, and 3 M of ammonium thiocyanate mixed with PD for 2 min and extracted for 2 min. The developed method was validated according to the ICH guidelines, the calibration curve was constructed with a correlation coefficient of 0.999 in a concentration range of 50-400 mu g/mL. The method was able to specifically detect and quantify PD in bulk with a % recovery 100.55% +/- 0.29 and in its commercial dosage form with a %recovery of 100.30 +/- 1.04.