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Recent papers have investigated the influence of sample composition on Flame Ionization Detector (FID) instrumentation used to measure total hydrocarbon content in exhaust emission samples. In this paper we describe experiments and results that further define these effects. Specially blended propane in air cylinders were crafted to provide a nominal 3 ppmC propane concentration with an oxygen content ranging from 17.5 vol % to 21 vol%. These cylinders were evaluated on multiple FID designs and then used to evaluate a strategy to correct the effects of the interaction. The study shows that, in general, most FID's behave similarly in response to changing oxygen content in the presence of hydrocarbon. Anomalies are discussed. The cylinders are then used to demonstrate that a proposed method for correcting the oxygen and hydrocarbon interaction is successful in reducing the effects.

Automotive emissions have been regulated to very low mass emissions. Various collection techniques have been utilized to measure the emitted gases. Some sample collection techniques utilize dilution gases that have concentrations below ambient air background values. For these applications analyzers with very low ranges have been produced. When using analyzers with ranges below 10 ppm, gas accuracy and impurities become very critical to the successful operation of these analyzers. A general demonstration of analyzer accuracy will be presented for various ranges. The availability and accuracy of the reference gases will be discussed. The relationship between the accuracy of the gas labeling and the analyzer's calibration accuracy will be evaluated. Gas delivery components can also affect the purity of zero gases and the accuracy of gas mixtures. Oxygen cleaned gas cylinder regulators will be compared to standard regulators for THC background contribution.