Development of microwave plasma proton transfer reaction mass spectrometry (MWP-PTR-MS) for on-line monitoring of volatile organic compounds: Design, characterization and performance evaluation.

Proton transfer reaction mass spectrometry (PTR-MS) is a revolutionary on-line VOCs monitoring method. In this study, a new microwave plasma-based proton transfer reaction mass spectrometry (MWP-PTR-MS) is developed. The MWP consists of a surfatron type resonator and a cooperative ion extraction device to achieve high efficiency production of hydronium ions. Non-local thermodynamic equilibrium water plasma is generated in a quartz tube at 200 Pa with 2.45 GHz microwave. Characters of MWP, such as emission spectroscopy, input power, dirty ion suppressing and ion extraction, are explored systematically. With the same test platform, MWP has a 7-fold increment of hydronium ion production rate than glow discharge source. The counts rate of hydronium ion is 8 × 10 cps with abundance of NO and O is less than 0.4% and 5% respectively. The performance of MWP-PTR-MS is validated by analysis of several chemicals and demonstration application is conducted. The instrument showed good linearity above 99% in the range of 4.5 × 10 to 4.5 × 10 mol/L. Benefited from the character of surface wave and 2.45 GHz microwave, MWP has high potential in improving the performance and reliability of current PTR-MS.