Ions were generated by a nanoelectrospray ionization (nanoESI) source (3000 V) using a chemically etched emitter (20 μm i.d.) connected to a 30 μm i.d. fused-silica capillary (Polymicro Technologies, Phoenix, AZ) through a zero volume stainless steel union (Valco Instrument Co. Inc., Houston, TX). Sample solutions were infused at a flow rate of 0.3 μL/min. Ions were introduced into the first stage of vacuum through a heated (130 °C) 500 μm i.d. stainless steel capillary (Figure 1A). After exiting the capillary, ions were accumulated and stored for 25 ms by an ion funnel trap (IFT, 950 kHz and ~200 Vpp) at 1.85 to 3.95 Torr and then released over 486 μs.64 (link) The ion inlet capillary was offset from the center axis of the IFT by 6 mm to minimize the transmission of neutrals through the IFT and conductance-limiting orifice, as well as to effectively eliminate gas dynamic effects in the SLIM chamber. Upon exiting the trapping region of the IFT, ions pass through a 2.5 cm long converging region of the IFT and are transported through a conductance-limiting orifice (2.5 mm i.d.) into the SLIM module chamber. The TW SLIM chamber was maintained at 2–4 Torr nitrogen filtered through hydrocarbon and moisture traps. A differential positive pressure of ~50 mTorr was also used to further prevent neutrals from entering the SLIM chamber. After drifting through the TW SLIM module, a 15 cm long rear ion funnel (820 kHz and ~120 Vpp) with a 23 V/cm DC gradient was used to focus the ion beam through a conductance limiting orifice (2.5 mm i.d.) into the differentially pumped region (460 mTorr) containing a short RF-only quadrupole (1 MHz and ~130 V). Ions are then transmitted into an Agilent 6224 TOF MS equipped with a 1.5 m flight tube (Agilent Technologies, Santa Clara, CA). Data were acquired using a U1084A 8-bit ADC digitizer (Keysight Technologies, Santa Rosa, CA) and processed using in-house control software written in C#.