The ion source was fabricated with two inlets for introducing samples in ambient conditions (Fig. ). The length and inner diameter (i.d.) of the stainless-steel capillary inlets are 10 and 0.25 mm, respectively. The HCD ion source is made up of two stainless steel metallic electrodes. An insulator composed of ceramic with a thickness of 5-6 mm separates the two electrodes. Inlet-1 is connected to the cathode, whereas inlet-2 is connected to the flange of the ion source that acts as an anode (Fig. ). Throughout the experiment, inlet-1 was used for ambient sampling while inlet-2 was closed. The cathode (length: 2 mm; i.d.: 2 mm) was connected to a high-voltage power supply (Pulse Electronic Engineering Co. Ltd, Chiba, Japan), while the anode (flange) was held at ground potential.