Proton Transfer Reaction Mass Spec(PTRMS)
Quick Specs
- Response time of 1 second
- Detection limit as low as 50 pptv
- Field and airplane deployable
EMSL's field-deployable Proton Transfer Reaction Mass Spectrometer (PTR-MS) is capable of real-time, online quantification of volatile organic compounds in air. The instrument provides an extremely fast response time of about one second, and detection limits for a one-second integration time range from 50 pptv to about 300 pptv, depending on the nature of the analyte.
Organic species are measured using chemical ionization mass spectrometry. H3O+ is used as the reagent ion and results in a soft ionization of most organic species with negligible fragmentation. The air sample is continuously drawn into a reaction chamber where it encounters the reagent ion. Organic species having a proton affinity greater than that of H2O will react with H3O+ in a proton transfer reaction:
R + H3O+ → RH+ + H2O
The major constituents of air do not react with H3O+. A small portion of the flow through the reaction chamber is sampled by a quadrupole mass spectrometer where the RH+ ions are mass filtered and detected by an ion multiplier. The amount of analyte (R) in the sample air is determined by a simple formula relating the H3O+ count rate, the RH+ count rate, the rate constant for the ion-molecule reaction, and a fixed reaction time. The rate constants for many of these reactions are known, but can also be calculated from theory.
The PTR-MS is ideally suited for performing fast real-time measurements of particular species that are known to be present in a mixture or that have unique masses in order to study a rapidly evolving temporal process. The instrument is built into an aerospace grade rack and has been successfully flown on a research aircraft to collect measurements of urban air pollution. The figure below illustrates its measurement capability. These data were collected when the PTR-MS was installed on the Battelle G-1 research aircraft during an air quality field experiment in Puget Sound during the summer of 2001. The PTR-MS is an enabling technology that will allow in situ studies of the fate and transformation of organic matter in the atmosphere not previously possible with older technologies.
All Related Publications Related Publications
- Probing Emissions of Military Cargo Aircraft: Description of a Joint Field Measurement Strategic Environmental Research and Development Program.
- Nitrate Ion Photochemistry at Interfaces: A New Mechanism for Oxidation of alpha-Pinene.
- The Time Evolution of Aerosol Composition Over the Mexico City Plateau.
- Measurements and Interpretation of the Effect of a Soluble Organic Surfactant on the Density, Shape and Water Uptake of Hygroscopic Particles.
- Distribution, Magnitudes, Reactivities, Ratios and Diurnal Patterns of Volatile Organic Compounds in the Valley of Mexico During the MCMA 2002 & 2003 Field Campaigns.