Enantiomeric assay of escitalopram S (+)‐enantiomer and its “in‐process impurities” using two different techniques

The enantiomeric purity of escitalopram oxalate ESC and its “in‐process impurities,” namely, ESC‐N‐oxide, ESC‐citadiol, and R (−)‐enantiomer were studied in drug substance and products using high‐performance liquid chromatography (HPLC)‐UV ( Method I ), synchronous fluorescence spectroscopy (SFS) ( Method IIA ), and first derivative SFS ( Method IIB ). Method I describes as an isocratic HPLC‐UV for the direct resolution and determination of enantiomeric purity of ESC and its “in‐process impurities.” The proposed method involved the use of α l ‐acid glycoprotein (AGP) chiral stationary phase. The regression plots revealed good linear relationships of concentration range of 0.25 to 100 and 0.25 to 10 μg mL −1 for ESC and its impurities. The limits of detection and quantifications for ESC were 0.075 and 0.235 μg mL −1 , respectively. Method II involves the significant enhancement of the fluorescence intensities of ESC and its impurities through inclusion complexes formation with hydroxyl propyl‐β‐cyclodextrin as a chiral selector in Micliavain buffer. Method IIA describes SFS technique for assay of ESC at 225 nm in presence of its impurities: R (−)‐enantiomer, citadiol, and N‐oxide at ∆λ of 100 nm. This method was extended to ( Method IIB ) to apply first derivative SFS for the simultaneous determination of ESC at 236 nm and its impurities: the R (−)‐enantiomer, citadiol, and N‐oxide at 308, 275, and 280 nm, respectively. Linearity ranges were found to be 0.01 to 1.0 μg mL −1 for ESC and its impurities with lower detection and quantification limits of 0.033/0.011 and 0.038/0.013 μg mL −1 for SFS and first derivative synchronous fluorescence spectra (FDSFS), respectively. The methods were used to investigate the enantiomeric purity of escitalopram.