Direct Injection MS Characterization

The direct injection MS was carried out on an AB Sciex 4000 QTrap system (AB Sciex, Framingham, MA) with an electrospray ionization source. MS analysis was performed under positive mode. The 20-µL sample was injected into this system. The mobile phase was 80% acetonitrile aqueous. The initial flow rate was 0.2 mL/min, decreased to 0.01 mL/min in 0.08 min, and then remained stable over the next 1.5 min. In the next step, flow rate was returned to 0.2 mL/min in 0.01 min and maintained for 0.5 min. The MS detection 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, 35 psi. Scan modes and parameters were set according to a previous study [25 (link)]. Analyst 1.6.0 software (AB Sciex) was applied to control system, align spectrum, and gather amino acid and carnitine/acylcarnitine data. ChemoView 2.0.2 (AB Sciex) was carried out for data preprocessing.