Analysis of Grape Volatiles Using Atmospheric Pressure Ionization Gas Chromatography Mass Spectrometry-Based Metabolomics.

Analysis of volatile compounds in fruits and plants can be a challenging task as they present in a large amount with structural diversity and high aroma threshold, the information on molecular ion can be very useful for compound identification. Electron ionization gas-chromatography-mass spectrometry (EI-GC-MS) which is widely used for the analysis of plant volatiles has a certain limitation providing the limited capability to characterize novel metabolites in a complex biological matrix due to hard fragmentation level. Atmospheric pressure ionization using APGC source in combination with high-resolution time-of-flight mass spectrometry (TOF-MS) provides an excellent combination of GC with high-resolution mass spectrometry. The APGC-MS approach provides several advantages over the conventional EI and CI based GC-MS techniques in metabolomics studies due to highly reduced fragmentation, which preserves molecular ion, and accurate mass measurement by HRMS allows to deduce the elemental composition of the volatile compounds. Moreover, the use of MSE mode provides spectral similarity to EI in high-energy mode which can be used for the further confirmation of metabolite identity. We describe an APGC-MS-based untargeted metabolomics approach with a case study of grape volatile compounds and the development of a spectral library for metabolite identification.