Miniature Mass Spectrometry for On-Site Analysis Using Self-Suction Sampling and α-Particle Ionization

Abstract The ion source is a key component of mass spectrometers, where electricity, lasers, and heat are typically used for converting molecules into ions; however, this poses a challenge due to the high-energy consumption, especially for portable miniMS systems in field environments. In this study, we report a field-deployable approach utilizing a miniature mass spectrometry (MS) system coupled with α-particle ionization and self-suction sampling. Without any external energy input, high-energy α-particles stably generated from radioactive sources (e.g., Am-241 and Th-232) directly ionize various ambient aerosol samples, which are introduced into the system via a self-suction effect under a slight differential pressure (∼0.3 kPa). A range of ion species, including radical cations, anions, and protonated ions, were observed. The underlying ionization mechanism is proposed to involve a complex cascade of processes, namely, α-particle impact, dissociative electron attachment, and subsequent chemical ionization. The practical utility of this miniMS system was unambiguously validated through the on-site detection of diverse real-world samples. For direct analyte measurement, acceptable relative standard deviations (RSDs) of <20% (n = 6), good quantitative linearity over more than 2 orders of magnitude, and low limits of detection at the ng/mL level were achieved. Overall, our experimental data demonstrated that the α-particle source not only serves as a compact, high-energy, and stable ionization platform for miniature MS in field environments but also offers a valuable tool for investigating fundamental gas-phase ion chemistry.