小型高性能质子转移反应飞行时间质谱仪的研制及其在呼吸气成分分析中的应用

研制可快速、在线分析挥发性有机物（volatile organic compounds, VOCs）的质谱仪器是现代气态有机质谱的重要发展方向。本研究自行研制了小型高性能质子转移反应飞行时间质谱仪（proton transfer reaction time of flight mass spectrometry, PTR-TOF MS），仪器采用结构简单可靠的空心阴极放电源作为水蒸气电离源，以产生水合质子；线性漂移管作为分子离子反应管。该离子源产生的水合离子纯度高，为水合离子与VOCs的分子离子反应提供可控的反应条件。传输接口部分使用射频四极杆作为离子导向装置，以提高离子传输效率；配合小尺寸飞行时间质量分析器，兼顾仪器的灵敏度与分辨率。质子转移反应的测定原理使该仪器可以分析除少数烷烃外的绝大多数VOCs，同时分析过程不受空气组分的影响。分子离子峰为主的产物离子形式使谱图便于解析，适合高通量分析。测试结果表明，该仪器在m/z 115处全高半峰宽（full width half maximum, FWHM）分辨率优于2 500，对丙酮、苯、甲苯的检出限在6×10^-12~9.6×10^-11 mol/mol之间。将该仪器应用于人体呼吸气的成分分析，取得了良好的结果。

Development of Small Sized High Performance Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF MS) and Its Application in VOCs Analysis in Exhaled Gas

Nowadays, trend of novel mass spectrometer development concentrates on fast, on-line analysis of samples with minor or without pretreatment. An important branch of modern mass spectrometer development is to build a fast and on-line instrument for volatile organic compounds (VOCs) analysis. In this study, a high-performance small size proton transfer reaction-time of flight mass spectrometer (PTR-TOF MS) was developed. The structure of the instrument was described in detail as well as the performance test and applications in exhaled gas analysis. The ion source of the described PTR-TOF MS utilized a simple structure hollow cathode discharge to produce hydronium ion. A linear drift tube was designed as the ion molecule reactor. The mass spectrum of reagent ion showed that the base peak of reagent ion was H₃O⁺ (m/z 19). Intensity of (H₂O)_nH₃O⁺ (n=1, m/z 37) was 5% of H₃O⁺ (m/z 19). The main pollution ion NO⁺ (m/z 30) was 0.5% of H₃O⁺ (m/z 19) which indicated that the purity of the ion source was good for proton transfer reaction. A direct current was arranged evenly across the whole reaction tube to maintain a consistent reaction E/N. The interface between ion source and TOF MS was a RF-only quadruple. The frequency and voltage of the RF-only quadruple were adjusted for the best transferring of VOCs ions. A set of focus lenses and collimation lenses was followed for ion beam refining before entering mass analyzer. The mass analyzer used in this instrument was a small sized time of flight mass spectrometer. The total length of the mass analyzer was 360 mm which ensured the small size of the instrument. The time of flight mass spectrometer used orthogonal acceleration, twin pulse, reflect second-order focusing was used to maximum the resolution. Experiment result showed that the full width half maximum m/z 115 is better than 2 500. The detect limit for acetone, benzene and toluene is from 6×10^-12 mol/mol to 9.6×10^-11 mol/mol. The instrument also shows good linearity between concentration 1×10^-8 mol/mol and 1×10^-6 mol/mol. The instrument was successfully applied to component analysis of human exhaled gas. Further works will be concentrated on the quantitative analysis of components of real samples. The developed high-performance small size PTR-TOF MS has potential in applications in environment, biology, petrochemical industry etc.