Design and Performance Optimization of a Portable VOCs Mass Spectrometer System

Due to their high reactivity, volatile organic compounds (VOCs) can engage in physical and chemical reactions with particulate matter in the atmosphere, leading to air pollution. Extended exposure to VOCs may result in various health concerns, including respiratory system problems, neurological effects, skin and eye irritation, and an increased risk of certain cancers. Traditional benchtop mass spectrometers possess the advantages of high sensitivity and rapid analysis capabilities, but the large size typically confines their applications to professional laboratories. To overcome this limitation, portable mass spectrometers are emerging as a new tool for in-situ analysis. In this study, a portable mass spectrometer based on discontinuous atmosphere pressure interface was developed, which combined with a sub-vacuum plasma ionization source. Ion trap, known for its small size and adequate performance, was adopted in this miniaturized mass spectrometer. This portable mass spectrometer features a total weight of about 4.6 kg, with the dimensions of 217 mm×162 mm×106 mm, and operates with a power consumption under 150 W. On this design, a fully metallic solenoid valve was selected as the core component to limit atmospheric pressure, eliminating the need for the rubber tubing used in traditional pinch valves. Compared to traditional pinch valves, this solenoid valve ensures a more stable airflow during experiments. As a result, the repeatability and environmental adaptability of the portable mass spectrometer were improved. A certain delay marked as radio freqency (RF) delay was introduced between the injection and cooling periods, and the RF-delay time was optimized. Frequency scanning mode and amplitude scanning mode were tested in parallel. Despite of a trade-off in size, amplitude scanning offered improved resolution, enabling the differentiation of ions with close mass to charge ratios. After systematic optimization, satisfactory performances in mass resolution and sensitivity were achieved. The mass resolution of the mass spectrometer for dimethyl carbonate was improved to 0.2 u (FWHM), and a sensitivity of 60 μg/m³ for naphthalene was achieved. The capability of mixed VOCs was also validated using dimethyl carbonate and trimethyl phosphate. This mass spectrometer developed in this study, characterized by its high portability and satisfactory performance, is expected to hold great potential for applications in VOCs analysis.