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GC/MS is the major analytical platform in plant metabolomics and is also applied for metabolomics studies in clinical biomarker discovery, disease diagnosis and toxicology. GC/MS is mainly used with electron impact (EI) and chemical ionization (CI) in combination with spectral libraries for compound identification In EI, fragmentation during ionization often impairs the identification of the molecular ion. The alternative ionization is APCI preserving the molecular ion information. When coupling GC/APCI to a TOF-MS, high resolution accurate mass and isotopic pattern data can be obtained for molecular formula determination. Derivatization reaction was done with methoxyamination and silylation. The samples were injected on a HP-5-MS column and analyzed by a temperature gradient of 5°C/min over 57 min (oven initial T= 70°C kept over 5 min). MS analysis was carried out using an ESI-TOF in positive mode in 50-1000 m/z. Human cerebrospinal fluid (CSF) extracts were prepared by cold methanol precipitation (2h) and centrifugation. The supernatant was evaporated under nitrogen and subsequently derivatized. The optimization, calculation of the analytical parameters and validation of the method was made with a standard mix of 35 compounds to cover a wider range of polarity and molecular weight. 26 of the 35 compounds were identified according to the molecular formula of the silylated derivatives with mass accuracies better than 3ppm and sigma fit values smaller than10mSigma. The developed method was applied to the analysis of human cerebrospinal fluid (CSF) samples. The analyses of a set of CSF samples will be considered as a future direction looking for new biomarkers and checking the potential of this new coupling.