A Novel Conjugated Octupole–Quadrupole Ion Guide Achieving High Transmission

Rationale Ion transmission efficiency from the atmospheric pressure ion source to the vacuum is critical for the sensitivity of mass spectrometers. In this study, we developed a novel conjugated octupole–quadrupole ion guide—the 8–4 pole ion guide—that achieves high transmission efficiency. Methods The dependence of signal intensity on parameters, including DC voltages, RF voltage applied to the 8–4 pole ion guide, and pressure within the ion guide, was measured. The transmission efficiency of the 8–4 pole ion guide was estimated from the ion current introduced into the ion guide and passing through the aperture downstream of the guide. The sensitivity of the mass spectrometer equipped with the 8–4 pole ion guide was evaluated using testosterone. Potential calculations and ion trajectory simulations were employed to better understand ion behavior within the 8–4 pole ion guide. Results The dependence of signal intensity on pressure within the 8–4 pole ion guide suggests that the device achieves high ion transmission in the pressure range of 100–200 Pa. The ion current introduced into the 8–4 pole ion guide was 1.8 nA, while the ion current passing through the downstream aperture was 1.0 nA, resulting in a transmission efficiency of 56%. The mass spectrometer with the 8–4 pole ion guide achieved a coefficient of variation of 2.9% for 1 pg/mL testosterone. The lower limit of detection for testosterone was 0.12 pg/mL. Conclusions We successfully developed a novel 8–4 pole ion guide. The high transmission efficiency, demonstrated by ion current measurements, and the enhanced sensitivity of the mass spectrometer equipped with this ion guide indicate that it can maintain high transmission efficiency even under a high inlet gas flow of 5 L/min.