Semi-preparative isolation and structural elucidation of an impurity in citalopram by LC/MS/MS

Two impurities were detected in citalopram bulk drug substance by HPLC analysis. A new LC–ESI/MS method was developed for the identification of impurities. One of the impurities was found to be unknown and has not been reported previously. The structure of the unknown impurity was proposed on the basis of MSn data obtained using ion trap mass analyzer and accurate mass obtained using Q-TOF mass analyzer. The impurity was isolated by semi-preparative HPLC. The structure of the impurity was confirmed as 1-(1,1-bis (4-fluorophenyl)-1,3-dihydroisobenzofuran-5-yl)-4-(dimethylamino) butan-1-one hydrobromide by using NMR and IR spectroscopy.