6430 triple quadrupole qqq mass spectrometer

Samples were analysed by an Agilent 1100 HPLC system coupled to an Agilent 6430 Triple Quadrupole (QQQ) mass spectrometer equipped with an electrospray ion source as described previously (2) . Chromatographic separation was performed on a Kinetex C18 column, using 0.1% formic acid in water (solvent A) and 0.1% formic acid in methanol (solvent B) as the mobile phase for binary gradient elution. The elution gradient was 18% B at 1 min, 90% B at 10 min, 100% B at 11 min, 100% B at 12 min, 18% B at 13 min, and 18% B at 20 min. The column flow rate was 0.3 mL/min; the column temperature is 40 °C, and the autosampler was kept at 10 °C. Selective reaction monitoring (SRM) transitions for targeted TCA cycle metabolites and their isotopically labelled versions are shown previously (2) . Data acquisition was performed using Agilent MassHunter Workstation Data Acquisition software. Metabolite quantitation of both unlabelled and labelled metabolites was carried out based on calibration curves obtained with unlabelled authentic standards and normalized against internal standards.