A Comparison of Photoionisation Detection Gas Chromatography with a Tenax GC Sampling Tube Procedure for the Measurement of Aromatic Hydrocarbons in Ambient Air

Abstract

Abstract Photoionisation detector/gas chromatography (PID/GC) provides an opportunity for direct measurement of aromatic hydrocarbons in ambient air at ppb levels without preconcentration. The use of a portable PID/GC instrument has been evaluated and compared with a Tenax GC sampling tube method. The minimum detectable concentration using PID/GC was determined to be 0.3 ppb for benzene and toluene and 1.0ppb for C8-alkylbenzenes. At high concentrations (<100ppm), linearity of detector response was maintained by reduction in sample injection volume. In addition, due to the specificity of the detector, the instrument was found to be suitable for the measurement of aromatic hydrocarbons in vehicle exhaust by direct injection without interference from water vapour. Significant difficulties in quantitative sampling of concentrations typical of industrial atmospheres (>1ppm), were found using the Tenax GC preconcentration method. On-site measurement of aromatic hydrocarbons at a busy urban road-side location was undertaken using the two techniques. Measured concentrations of benzene and toluene compared favourably although the PID/GC technique was found to be inconsistent in the detection of low ambient concentrations of higher alkylbenzenes. However it is evident that rapid and direct measurement of a wide range of concentrations can be achieved using the PID/GC techniques which complement and in some cases supercede existing preconcentration techniques.