Segmented-Field-Gradient-Focusing Ion Guide for Simultaneously Improved Ion Transfer across a Wide Mass Range and Enhanced Sensitivity

The sensitivity of the atmospheric pressure ionization mass spectrometer (API-MS) has been improved owing to the advancement in the atmospheric pressure interface. However, ion scattering losses in the first vacuum chamber undermine this improvement. In this work, a novel multipole ion guide, called a segmented-field-gradient-focusing ion guide (SFGF-IG), was developed to address these losses, especially caused by the asymmetric-shaped supersonic jet generated by a slot-shaped inlet. The SFGF-IG combined a dodecapole (65 mm in length) and a quadrupole (125 mm in length), with each segment having its tilt angle optimized. By analyzing three different ion trajectory conditions, “Transmitted”, “Reflected”, and “Absorbed″, the key factors affecting the ion transfer in the SFGF-IG were investigated. Here, this analytical method for developing a high-performance ion guide was expanded to account for the influence of background gas. This revised method provides a framework for understanding the dominant mechanism that influences ion transfer within high-performance ion guides under complex background gas flow. Results showed that the SFGF-IG reduced ion scattering losses in the first vacuum chamber, which allowed the greater gas-throughput slot-shaped inlet to increase the API-MS sensitivity. Compared with the conventional ion funnel, the SFGF-IG demonstrated a significantly reduced low-mass discrimination effect and improved ion transfer across a wide mass range (100–2000 m/z), enabling simultaneous analysis of high-, medium-, and low-mass ions. Moreover, to verify the actual performance of the SFGF-IG, it was integrated into a home-built quadrupole-linear ion trap tandem MS (Q-LITMS) equipped with a slot-shaped inlet. The instrument detection limit (IDL) of the reserpine reached 0.15 fg (RSD 6.08%), two-fold lower than the conventional Q-LITMS configuration (0.3 fg and RSD 11.1%). This work provides a complete development approach for a high-performance ion guide to reduce ion scattering losses and further enhances the sensitivity of laboratory-scale MS.