The application of total hydrocarbon flame ionization detectors to the analysis of hydrocarbon mixtures from motor vehicles,with and without catalytic emission control

The successful application of total hydrocarbon analyzers to the analysis of hydrocarbon mixtures requires linear response with respect to a single calibration compound. Flame ionization detectors configured for total hydrocarbon analysis (premixed flames) do not respond in the same manner to all hydrocarbon species. A discussion of the source of the phenomena is presented. An investigation is presented illustrating the problem in application of the technique to total hydrocarbon analysis of motor vehicle exhaust samples. The response of the nine most abundant auto exhaust hydrocarbons relative to propane, the compound commonly utilized for calibration, is defined for two commercial analyzers. The hydrocarbons selected for the investigation include methane, isopentane, isooctane, ethylene, propylene, acetylene, benzene, toluene, and p-xylene. Analytical error predictions are made based on calculations utilizing the relative response and abundance of these hydrocarbons in samples from motor vehicles. Both catalyst equipped and non-catalyst vehicles are used as sources. The validity of the calculated predictions is empirically verified by comparison with total hydrocarbon levels obtained by summing the concentrations of the individual hydrocarbons obtained with gas chromatography. Procedures to minimize the potential error are presented. The degree of improvement in hydrocarbon response linearity attainable through detector sample flow rate reduction is presented.