APGC-qTOF Analysis. The presence of EC in the extracts of plasma samples were further confirmed by accurate mass measurement using Waters Atmosphere Pressure Gas Chromatograph (APGC) coupled with a Xevo G2 QTOF time-of-flight mass spectrometer (Waters, Milford, MA). Samples (1 µL) was injected onto a DB-WAXUI column (Agilent, 30 m x 0.25 mm x 0.25 µm) with a pulsed splitless mode with pulse pressure held at 32 psi during the first 1.2 min. The oven was initially held at 50°C for 1.2 min, then ramped to 250°C at a rate of 20°C/min with a final hold of 1 min. Sample flow underwent atmospheric pressure ionization in positive mode with nitrogen gas temperature of 220°C at the interface. A 2-mL glass vial of methanol containing 10% acetic acid was situated on lower level of the source housing to supply polar vapor to assist ionization. Corona pin current was set at 3 µA, sampling cone at 5 V, and extraction cone at 4 V. Source temperature was set at 150°C.