Numerical Simulation and Experimental Study of a Dual-Ionization Source (PI/EI) Quadrupole Mass Spectrometer Based on the CFD–DSMC Method

Abstract

Background

Online analysis of complex gas mixtures is often hindered by spectral congestion resulting from extensive fragmentation in traditional electron ionization (EI) sources. Although photoionization (PI) provides clean mass spectra by preserving molecular ion integrity, its comprehensive detection is limited by an inherent ionization selectivity toward species with low ionization energies.

Methods

To address these challenges, a dual-ionization source quadrupole mass spectrometer (DISQMS) integrating PI and EI was developed. Its design and optimization were guided by a multiphysics ion trajectory simulation method coupling continuum-rarefied flow fields with electric fields. The flow field, spanning from the sampling capillary to the quadrupole mass analyzer chamber, was numerically simulated using a hybrid computational fluid dynamics–direct simulation Monte Carlo (CFD–DSMC) method.

Results

Guided by the simulation, the key instrumental parameters were systematically optimized, and the reliability of the simulation model was validated experimentally. During the detection of acetone, benzene, and air mixtures, clean organic spectra were obtained in PI mode, whereas comprehensive detection of inorganic gases with high ionization energies (e.g., N₂ and O₂) and detailed fragment-ion information were achieved in EI mode.

Conclusions

A DISQMS was developed and validated, and a multiphysics ion trajectory simulation framework was proposed to numerically optimize the instrument's sensitivity. It was demonstrated that complementary detection of organic and inorganic species is achieved through the dual-mode capability. Specifically, spectral interpretation and molecular structure elucidation are effectively facilitated by combining the detailed fragment-ion information from EI with the clean molecular ion data from PI.