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Detection of trace hydrocarbons in flames using direct sampling mass spectrometry coupled with multilinear regression analysis

Detection of Trace Hydrocarbons in Flames Using Direct Sampling Mass Spectrometry Coupled with Multilinear Regression Analysis

Maria A. Puccio and J. Houston Miller
Analytical Chemistry 2010 82 (12), 5160-5168

DOI: 10.1021/ac1003823

 

Concentration contours (top, from left to right) of acetylene, butadiene, 1-buten-3-yne, and butadiyne and (bottom, from left to right) of benzene, toluene, phenylacetylene, and naphthalene.

A technique for the determination of species’ concentrations from the molecular growth regions of flames is presented. Samples are obtained by microprobe extraction from a nitrogen-diluted, methane/air, nonpremixed laminar flame supported on a coannular burner. Quantification of measurements is accomplished by doping the flame’s fuel flow with argon at a level to match that in the laboratory’s air. A library of 70 eV fragmentation patterns for several flame species is used in conjunction with a simplex algorithm to analyze mass spectra obtained at each flame location. Each fragmentation pattern is normalized for its integrated intensity and its ionization cross-section relative to argon. This technique provided sub-part-per-million sensitivity of a large range of major and minor carbon-containing species ranging in size from C2 to C12 hydrocarbons. This flame can be acoustically forced to oscillate at a frequency emulating natural flame flickering behavior. Time-resolved measurements are obtained using a modified quartz microprobe synchronized to open and close with the flame oscillations. The near real-time sampling and analysis time and the relatively high sensitivity make this technique preferable to other extraction-based flame measurements.

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