Validated LC Method for Determination of the Enantiomeric Purity of Montelukast Sodium in Bulk Drug Samples and Pharmaceutical Dosage Forms

A new and accurate chiral liquid chromatographic method has been developed for determination of the enantiomeric purity of montelukast sodium (R enantiomer) in bulk drugs and dosage forms. Normal phase chromatographic separation was performed on an immobilized amylose-based chiral stationary phase with n-hexane-ethanol-1,4-dioxane-trifluoroacetic acid-diethylamine 65:25:10:0.3:0.05 (v/v) as mobile phase at a flow rate of 1.0 mL min⁻¹. The elution time was approximately 15 min. The resolution (R S) between the enantiomers was >3. The mobile phase additives trifluoroacetic acid and diethylamine played a key role in achieving chromatographic resolution between the enantiomers and also in enhancing chromatographic efficiency. Limits of detection and quantification for the S enantiomer were 0.07 and 0.2 μg, respectively, for a test concentration of montelukast sodium of 1,000 μg mL⁻¹ and 10 μL injection volume. The linearity of the method for the S enantiomer was excellent (R ² > 0.999) over the range from the LOQ to 0.3%. Recovery of the S enantiomer from bulk drug samples and dosage forms ranged from 97.0 to 103.0%, indicative of the high accuracy of the method. Robustness studies were also conducted. The sample solution stability of montelukast sodium was determined and the compound was found to be stable for a study period of 48 h.