On-line Analysis of Organic Compounds in Diesel Exhaust Using a Proton Transfer Reaction Mass Spectrometer (PTR-MS)

Journal Article · Mon Aug 01 00:00:00 EDT 2005 · International Journal of Mass Spectrometry, 245(1-3):78-89

DOI:https://doi.org/10.1016/j.ijms.2005.05.009· OSTI ID:876897

Jobson, B Tom T; Alexander, M Lizabeth; Maupin, Gary D; Muntean, George G

Chemical ionization mass spectrometry using H3O+ proton transfer in an ion drift tube (PTR-MS) was used to measure volatile organic compound (VOC) concentrations on-line in diesel engine exhaust as a function on engine load. The purpose of the study was to evaluate the PTR-MS instrument as an analytical tool for diesel engine emissions abatement research. Measured sensitivities determined from gas standards were found to be between 30% and 100% greater than calculated sensitivities. A slight humidity dependent sensitivity was observed for non-polar species, implying that reactions with H+(H2O)2 were important for some organics. The mass spectra of diesel exhaust were complex but displayed a pattern of strong ion signals at 14n+1 (n=3..8) masses, with a relative ion abundance similar to that obtained from electron impact ionization of alkanes. Laboratory experiments verified that C8-C16 n-alkanes and C8-C13 1-alkenes react with H3O+ in dissociative proton transfer reaction resulting in alkyl cation ion products, primarily m/z 41, 43, 57, 71 and 85. Monitoring the sum of these ions signals may be useful for estimating alkane emissions from unburnt diesel fuel. Alkane fragmentation likely simplified the diesel exhaust mass spectrum and reduced potential mass interferences with isobaric aromatic compounds. It is shown that the relative abundances of VOCs changed as a function of engine load. Concentrations of aldehydes and ketones dominated those of aromatic species with formaldehyde and acetaldehyde estimated to be the most abundant VOCs in the PTR-MS mass spectrum at all engine loads. The relative abundances of benzene and toluene increased with engine load indicating their pyrogenic origin. The relative abundance of alkanes, aromatics, aldehydes, and alcohols was broadly consistent with literature publications of diesel exhaust analysis by gas chromatography. About 75% of the organic ion signal could be assigned. On line analysis of diesel exhaust using this technology may be valuable tool for diesel engine emission research.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 876897
• Report Number(s): PNNL-SA-44230; 3364; TRN: US200608%%280
• Journal Information: International Journal of Mass Spectrometry, 245(1-3):78-89, Vol. 245, Issue 1-3
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
ACETALDEHYDE
ALDEHYDES
ALKANES
BENZENE
CATIONS
DIESEL ENGINES
DIESEL FUELS
GAS CHROMATOGRAPHY
ION DRIFT
MASS SPECTRA
MASS SPECTROMETERS
MASS SPECTROSCOPY
ORGANIC COMPOUNDS
PROTONS
TRANSFER REACTIONS
VOLATILE MATTER
VOC
hydrocarbons
PTR-MS
diesel exhaust
chemical ionization
Environmental Molecular Sciences Laboratory