Gc ms metabolite mass spectral database

Sample preparation for GC–MS was performed as described previously ^{20 (link)}. In short, 50 μl of plasma were mixed with the extraction solvent containing the internal standard (2-isopropylmalic acid). After centrifugation, the supernatant was collected and dried with a centrifugal evaporator. After two derivatization procedures (oximation and trimethylsilyl derivatization), the extract was injected into the GC–MS system. GC–MS measurement using GCMS-QP2010 ultra (Shimadzu Corp., Kyoto, Japan) was performed according to a previous study^{20 (link)}. Chromatogram acquisition, detection of mass spectral peaks, and their waveform processing were performed using Shimadzu GC/MS solution software Version 2.71 (Shimadzu Corp., Kyoto, Japan). Small polar metabolites were identified using a commercially available GC–MS Metabolite Mass Spectral Database (Shimadzu Corp., Kyoto, Japan). Peak area of each metabolite was calculated, and then normalized using the internal standard peak. In the analysis of the institutional cohort, we evaluated the actual concentration of each sample by using a single-point calibration curve derived from concentration-determined D-Fructose 13C6 (ISOTEC, Miamisburg, OH, USA).

The GC-MS metabolomics data were analysed using the Shimadzu GCMSsolution software Version 2.53 (Shimadzu, Kyoto, Japan). The retention time correction of detected peaks was performed by adjusting it with the retention time of a standard alkane series mixture (C₁₀ to C₄₀) in the automatic adjustment of retention time (AART) function of the Shimadzu GCMSsolution software Version 2.53 (Shimadzu, Kyoto, Japan). Low-molecular-weight metabolites were identified by a commercially available GC/MS Metabolite Mass Spectral Database (Shimadzu Co., Kyoto, Japan). The GC/MS MS Metabolite Mass Spectral Database contained a mass spectral library (method files that specified the above-described analytical conditions) and the parameters for data analysis of 178 compounds (amino acids, fatty acids, and organic acids). A similarity index was calculated based on retention time and the confirmed ion and fragmentation pattern obtained in the mass spectrum of the low molecular weight metabolites. Peaks with a similarity index of less than 80 were processed as unknown molecules, while peaks with a similarity index more than 80 were identified metabolites. The peak height of 2-isopropylmalic acid was used as an internal standard to perform the semi-quantitative assessment (the peak height of each quantified ion was calculated and normalised using the peak height of internal standard).