Impurity profiling of pholcodine by liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS)

Previously, a dimorpholinoethyl pholcodine manufacturing impurity was reported to be present in some samples of pholcodine. Apart from this impurity and morphine, other unknown impurities were detected in all the samples analysed by HPLC and micellar electrokinetic capillary chromatography. In this study, liquid chromatography mass spectrometry (LC-MS) analysis of samples of pholcodine showed that two of the previously unidentified compounds had mass spectra with molecular ions which differed from pholcodine by 16 amu. From this observation and other experimental data it was concluded that they are hydroxy derivatives of pholcodine. 10-S-hydroxy-pholcodine, which was synthesized by the oxidation of pholcodine with chromic acid, had the same chromatographic properties as one of these compounds. An early eluting compound in the LC-MS chromatograms of pholcodine was identified as pholcodine-N-oxide by matching chromatographic and mass spectral data of a synthesized pholcodine-N-oxide standard. The reaction of pholcodine with m-chloroperoxybenzoic acid not only produced the mono N-oxide, but also pholcodine-di-N,N'-oxide.