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 -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 for ESC and its impurities. The limits of detection and quantifications for ESC were 0.075 and 0.235 μg mL , 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 for ESC and its impurities with lower detection and quantification limits of 0.033/0.011 and 0.038/0.013 μg mL for SFS and first derivative synchronous fluorescence spectra (FDSFS), respectively. The methods were used to investigate the enantiomeric purity of escitalopram.