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.