Design and characterization of a compact photoionization toroidal ion trap mass spectrometer with MCP detection

A miniature photoionization toroidal ion trap (TorIT) mass spectrometer prototype was developed for the analysis of volatile organic compounds (VOCs) in ambient air. The TorIT analyzer features a simplified configuration comprising two planar and two ring electrodes, enabling efficient ion trapping and mass analysis in a compact structure. A microchannel plate (MCP) detector was strategically used to capture ions radially ejected from the trap, with its geometry well-matched to the TorIT design. These two modules were integrated into a compact assembly with an overall length of 50 mm. The entire system exhibits excellent pressure tolerance, allowing for stable operation at elevated pressures up to 0.11 Pa. To address background noise from MCP operation under high pressure and UV scattering, we implemented a discontinuous ionization strategy coupled with optimized signal filtering, significantly improving the quality of the ion peaks. During direct atmospheric sampling through a 75 μm capillary, the PI-TorIT instrument achieves sensitive VOC detection with a demonstrated limit of detection of 483 ppbv for anisole. The successful integration of the TorIT analyzer and MCP detector may present a viable approach for developing compact mass spectrometers.