In order to determine an empirical flow rate of the analyte of interest, the flow rate of air through inlet-1 was calculated, and the calculated flow rate was found to be 360 mL/min . The ions generated in the HCD ion source were transmitted to the S-lens of a linear ion trap mass spectrometer (LTQ XL, Thermo Scientific, San Jose, CA, USA) using a stainlesssteel transfer tube. In the MS's initial pumping stage, a rotary vane pump was employed to keep the pressure at 1 Torr. It should be noted that running an ion trap mass spectrometer properly necessitates a high vacuum environment.