TD GC-MS and UPLC-MS methods to discover differentially expressed metabolites in sebum

Sebum is a lipid-rich biofluid produced by the sebaceous glands which are found in high abundance in areas where hair is present, along the neckline, the ‘T’-area of the face and on the upper back. Recent work has shown that sebum can be used in mass spectrometry-based metabolomics experimental workflows to identify metabolic changes that occur in individuals who are infected with the SARS-CoV-2 virus, Parkinson’s disease and REM-sleep Behavioural Disorders (RBD) when compared to healthy non-disease controls. We describe here standard operating protocols that can be used to analyse sebum that has been collected on gauze or cotton buds using two common and applicable hyphenated mass spectrometry (MS) methods, namely Thermal Desorption Gas Chromatography-Mass Spectrometry (TD GC-MS) and Ultra High Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS). For TD GC-MS the sebum samples are analysed directly with no sample preparation requirements and for UPLC-MS we detail the extraction process for sebum prior to data acquisition. The methods are demonstrated with results from sebum obtained from in-lab healthy volunteers to permit experiments in laboratories with access to either or both of the utilised chromatography-mass spectrometry methods.