Improving the efficiency of soft electron ionization by using the oscillatory movement of electrons

In process analytical chemistry, mass spectrometry analysis using a soft electron ionization (EI) source has qualitative advantages. However, the relatively small ionization cross-section of soft EI leads to lower sensitivity. To address this issue, a novel method has been developed to enhance the sensitivity of soft EI by utilizing a dual electron repeller and an ionization chamber to form a U-shaped electric field, causing electrons to oscillate within the field and effectively increasing the electron collision cross-sectional area. By combining with an electron lens, the virtual cathode effect at low electron energy can be reduced or even eliminated, thereby improving ionization efficiency. This method has resulted in a significant increase in signal intensity for m/z 18(H2O), with a factor of 4.2 at an electron energy of 25 eV and a factor of 3.75 at 20 eV, compared to the electron receiving mode. Additionally, it reduces the required emission current, which is beneficial for prolonging the life of the filament. The proposed technique is expected to expand the application of soft EI, particularly for rapid online analysis in process analytical chemistry such as catalyst research and chemical reaction process monitoring.