Citalopram EP Impurity C ; Citalopram USP Related Compound C ; 3-Oxo Citalopram ; 1-[3-(Dimethylamino)propyl]-1-(4-fluorophenyl)-1,3-dihydro-3-oxo- 5-isobenzofurancarbonitrile; 1-(3-(Dimethylamino)propyl)-1-(4-fluorophenyl)-3-oxo-1,3-dihydroisobenzofuran-5-carbonitrile ; 1440961-11-4 (Oxalate)