Analysis of ceramides in cosmetics by reversed-phase liquid chromatography/electrospray ionization mass spectrometry with collision-induced dissociation.

A rapid, sensitive and selective method involving reversed-phase liquid chromatography (LC) with electrospray ionization (ESI) mass spectrometry (MS) was employed for determination of commercial ceramides in cosmetics for quality control of the product formulation. Using this LC/ESI-MS technique, simultaneous separation and characterization of ceramides and an impurity substance were possible. Informative fragmentation patterns were obtained by employing LC/ESI-MS in both positive and negative ionization modes to identify the structures of both sphingoid base and N-acyl chains of ceramides, and also of an impurity. The combination of positive and negative mass spectra can be used for unambiguous confirmation of ceramides and for characterization of unknown species. In-source collision-induced fragmentation resulted in characteristic product anions for the ceramides containing a phytosphingosine moiety at m/z 267, 255 and 225, and for those with a sphingosine moiety at m/z 263 and 237, regardless of the length of the fatty acyl chains. The detection limit was about 0.5 pmol in selected-ion monitoring mode. Quantification using internal standards showed good linearity and a relative standard deviation of 4%. These ceramides were more sensitively detected in positive than in negative ion mode.