Suitability of direct reading instruments for the measurement of VOC concentrations in emission test chambers

Online VOC analyzer nowadays receive an increased attention in the field of emission testing. These instruments are not specific for a single compound and therefore show a sum value of all detectable VOC. To test whether the sum value of one detector is comparable to that of either another detector or a Tenax measurement several volatile organic substances were injected into a 1 m³ chamber and the resulting chamber concentration was determined with a flame ionization detector (FID), a photoacoustic detector (PAD) and sampling on tenax tubes. Depending on the type of test compound large differences in the determined concentrations were observed The alkanes could be measured with sufficient comparability by both detectors, for aromatic compounds like toluene the FID showed, as expected, a six times higher sensitivity.