Quantitative Metabolomics by Direct Injection MS

The direct injection MS was used for quantitative metabolomic analysis on an AB Sciex 4000 QTrap system (AB Sciex, Framingham, MA) coupled with an electrospray ionization source, and the MS analysis was conducted under positive mode. A sample volume of 20 μL was injected into the system. The 80% acetonitrile aqueous was used as mobile phase. An initial flow rate was set to be 0.2 mL/min. Flow rate was decreased to 0.01 mL/min within 0.08 min, and remained stable until 1.5 min. Subsequently, the flow rate reverted back to 0.2 mL/min within 0.01 min, and maintained for 0.5 min. MS parameters were set as follows: ion spray voltage 4.5 kV, curtain gas pressure 20 psi, auxiliary gas temperature 350 °C. Sheath and auxiliary gas pressure was set at 35 psi. The scan modes and scan parameters were referred to previous report^{19 (link)}. Analyst 1.6.0 software (AB Sciex) was applied to control system, align spectrum, and collect MS data. ChemoView 2.0.2 (AB Sciex) was used for absolute quantification purposes.