Analysis of human saliva metabolome by direct immersion solid-phase microextraction LC and benchtop orbitrap MS

Background: Saliva samples collected from one 58 year old male and one 35 year old female during 7 days of fasting were analyzed by direct immersion of both CI8 and mixed-mode biocompatible solid-phase microextraction fibers, in combination with a LC-MS method using a benchtop orbitrap instrument in both positive and negative ionization modes, in order to evaluate the difference in terms of metabolite coverage. Results: The mixed-mode coating provided better results, with the simultaneous extraction of a higher number of both hydrophilic and hydrophobic metabolites. The ability of detected features to distinguish differences between the individuals and changes in saliva metabolome induced by diet was also demonstrated. Conclusion: Saliva may be useful for medical diagnostics as it is non-invasive. The use of biocompatible solid-phase microextraction fibers can play an important role as an alternative sample preparation method for untargeted LC-MS metabolomics studies on human saliva because it provides simultaneous extraction of metabolites with a wide range of polarity, thus allowing the detection of changes in metabolic pathways with unsupervised statistical analyses.