5977a quadrupole mass selective spectrometer

The details regarding GC-MS analysis have been previously described [17 (link)]. Briefly, GC-MS analysis of metabolites in plasma was carried out using an Agilent Technologies 7890 N gas chromatograph coupled to an Agilent Technologies 5977A quadrupole mass selective spectrometer with a triple-axis detector (Agilent, Palo Alto, CA) operated in electron ionization mode at 70 eV with a mass scan range of m/z 50–800. Derivatized samples were separated on a VF-WAX column (Agilent Technologies, Middelburg, The Netherlands) with an oven temperature ramp from 50 °C to 230 °C. The carrier gas was helium set at constant flow mode (1.0 mL/min). The identification of each metabolite in the samples was confirmed by comparing their relative retention times and mass spectra with those of authentic standard compounds. The relative levels of metabolites were calculated by comparing their peak areas to that of the internal standard compound.
Fatty acid desaturase activities and elongase activities were obtained indirectly by calculating fatty acid ratios of products to precursors. The equations are as follows: C16 Δ9-desaturase = Palmitoleic acid/Palmitic acid; C18 Δ9-desaturase = Oleic acid/Stearic acid; Δ6-desaturase = γ-Linolenic acid/Linoleic acid; Elongase activity = Stearic acid/Palmitic acid.

The details of GC-MS have been previously published [16 (link)]. Briefly, all analyses were performed on an Agilent Technologies 7890 N gas chromatograph coupled to an Agilent Technologies 5977A quadrupole mass selective spectrometer with a triple-axis detector (Agilent, Palo Alto, CA) in the electron ionization mode (70 eV) and full scan monitoring mode (m/z 50–800). Derivatized samples were separated on a VF-WAX column (Agilent Technologies, Middelburg, Netherlands) with helium as the carrier gas and a temperature ramp from 50 °C to 230 °C. Metabolites in the samples were identified by comparing their relative retention times and mass spectra with those of authentic reference standards. The relative metabolite levels were calculated by comparing their peak areas to that of the internal standard compound.