A prototype low-pressure assisted microwave plasma ionization mass spectrometry for on-line monitoring of organic and inorganic hazardous compounds simultaneously: Design and feasibility validation

Abstract

Background

The detection of harmful atmospheric gases, including inorganic small molecules (e.g., hydrogen sulfide, H₂S) and volatile organic compounds (VOCs) such as aromatic hydrocarbons, is crucial due to their involvement in photochemical reactions that generate secondary pollutants like ozone and secondary organic aerosols. Current mass spectrometry-based techniques, including PTR-MS, SPI-MS, and SIFT-MS, are limited in their ability to simultaneously and sensitively detect a broad spectrum of these compounds due to significant variations in their physicochemical properties.

Results

This study developed a low-pressure assisted microwave plasma ionization time-of-flight mass spectrometer (LAMP-TOFMS), which features a novel coaxial three-metal-tube design adapted from atmospheric-pressure microwave plasma torch technology. Operable under low-pressure conditions (10–1000 Pa), the LAMP ion source employs multiple ionization mechanisms, including Penning ionization and charge transfer. The system was optimized for key parameters such as focusing electrode voltage, microwave power, and gas flow. LAMP-TOFMS achieved sub-ppbv detection limits, a broad linear dynamic range, and high stability, enabling the detection of challenging compounds, including H₂S, cyclohexane, and n-heptane. It was successfully applied for the quantification of odorous compounds around a pig farm.

Significance and novelty

To our knowledge, this is the first study to develop a low-pressure microwave plasma ionization source capable of simultaneously detecting organic and inorganic hazardous gases in real-time. Compared to conventional methods, LAMP-TOFMS demonstrates superior sensitivity, rapid response, and broader compound coverage. This innovative approach offers a transformative solution for comprehensive atmospheric monitoring, with significant implications for air quality and environmental health research.