A novel continuously curved planar hexapole traveling-wave ion guide: structure and performance analysis

Mass spectrometry (MS) is a powerful technique for qualitative and quantitative analysis and has been widely used in analytical chemistry, life sciences, medicine, food safety, and environmental monitoring. Ion guides are key components of MS instruments, among which traveling-wave ion guides offer high ion transmission efficiency and broad transmission bandwidth. They can also serve as ion mobility devices to provide complementary structural information. However, conventional traveling-wave ion guides are prone to the racetrack effect at bends, while RF potential barriers formed in the curved regions can cause ion loss. To address these issues, a continuously curved planar hexapole traveling-wave ion guide is proposed in this work. The number of RF electrodes and the RF feeding scheme were optimized through numerical simulations. The second RF driving mode of the hexapole electrode array formed a single ion channel, thereby suppressing the racetrack effect, and the continuous arrangement of RF electrodes in the curved section eliminated the RF potential barrier. Comparisons of different bend configurations showed that the 180° bend structure with four traveling-wave electrodes achieved the highest overall transmission efficiency. The effects of operating parameters were systematically investigated and optimized. Lower traveling-wave amplitudes and higher traveling-wave frequencies improved ion separation capability, whereas ion trapping occurred below 10 kHz. The proposed ion guide extends the ion mobility path within a compact PCB-based structure and enables synchronous co-directional transmission of both positive and negative ions.