Hybrid Ion Guide with Continuous Electric Field Transition from Dipole to Hexapole Fields for Wide m / z Bandwidth and High Transmission Efficiency

Abstract

Boosting ion transmission efficiency in the rough vacuum region is an important issue in atmospheric pressure mass spectrometry (API-MS). In this work, a hybrid ion guide (HIG) is proposed to enhance ion transmission efficiency and suppress the mass discrimination effect within rough vacuum environments. The HIG is constructed with discrete double-helix electrodes and a segmented hexapole assembly. Benefiting from the smooth continuous transition from the dipole field to the hexapole field, the device exhibits weakened fringe electric fields and superior ion-focusing capability. The central axial potential well of the HIG is shallow, which facilitates efficient transmission of low m/z ions. Fabricated via printed circuit board (PCB) technology, the HIG was integrated into a nanoESI-TOF-MS platform for experimental characterization. Experimental results show that at an RF voltage of 220 Vpp, the signal intensity ratio of caffeine ions (m/z = 195) to reserpine ions (m/z = 609) increases from 1.2% with the ion funnel (IF) to 43.1% with the HIG, demonstrating that the HIG has a wider m/z bandwidth. Moreover, relative to the discrete-double-helix ion funnel (DDH-IF), the HIG achieves improved instrumental sensitivity: the signal intensities of caffeine ions and reserpine ions are maximally enhanced by 2.2 and 4×, respectively. By realizing a continuous electric field transition across the first-to-second vacuum interface, the HIG offers a novel strategy for the development of continuous ion-transfer systems compatible with atmospheric pressure ionization mass spectrometry.