Evaluation of a Proton Transfer Reaction Mass Spectrometer for Analysis of Mobile Source Air Toxics in Engine Exhaust

Under the Clean Air Act, the U.S. Environmental Protection Agency has identified 21 Mobile Air Source Toxics. Because no truly portable, real-time method exists for the determination of these compounds in engine exhaust, there is an opportunity for the application of portable miniature mass spectrometry coupled with proton transfer reaction ionization (PTR-MMS) to such an analysis. The MMS utilizes a miniaturized cylindrical ion trap mass analyzer capable of rapid and sensitive analyses, including tandem mass spectrometry. The PTR ionization technique is well suited to the analysis of volatile organic compounds in air, although it has only been used in conjunction with linear quadrupole mass analyzers to date. The overall objective of this research project is the design and evaluation of an MMS-based, on-vehicle, real-time analysis technique. The specific goals include: (1) design of the gas-phase sample inlet; (2) evaluation of a PTR ionization source; (3) design of the interface of the PTR source with the developed MMS instrument; and (4) design of a software system that will provide instrument control and data acquisition. The results of the Phase I work will be summarized in a Phase I report. The instrument components will be evaluated based on performance including reproducibility, sensitivity, sampling frequency, and limit of detection. Phase I will demonstrate the feasibility of the proposed analytical system, and Phase II will be aimed at development of a prototype system. This includes an on-vehicle MMS-based instrument housed in a rugged package, direct gas-phase sampling port(s), and a robust software package for control and data acquisition. Because there are many applications for portable, real-time analyses, Griffin Analytical Technologies is pursuing the commercialization of MMS instrumentation, including the PTR-MMS system evaluated in this work.