Structure identification of unknown impurity in drug substance of escitalopram

Objective: To identify one unknown impurity in drug substance of escitalopram.Methods: The structure of the studied impurity was identified by LC-MS(MSn)on-line,and was further confirmed by preparative HPLC isolation and subsequent NMR analysis.Finally,the mechanism of the formation of the impurity was revealed with regard to product process,and the impurity was successfully avoided in the final product by process control.Results: The studied impurity was identified as(S)-3-(5-cyano-1-(4-fluorophenyl)-1,3-dihydroisobenzofuran-1-yl)-N-ethyl-N,N-dimethylpropan-1-aminium.Conclusion: The study provided valuable indications for both process development and quality study of drug substance of escitalopram.