Quantitative analysis of trace mixtures of toluene and xylenes by CO2 laser photoacoustic spectrometry

CO 2 laser photoacoustic spectroscopy was used for quantitative analysis of a multicomponent gaseous mixture of pollutants with similar chemical structures (toluene, ortho -, para - and meta -xylenes) in trace concentrations (50–700 ppm). The agreement with the results of gravimetric measurements was better than 5% in most cases. The following detection limits were found for this method in the given arrangement: 3.57±0.04 ppm for toluene, 1.82±0.02 ppm for o -xylene, 1.00±0.01 ppm for p -xylene and 2.86±0.04 ppm for m -xylene. Determination of the concentration using the classical least squares method was compared with a method based on the principle of calculation of the lowest component entropy. While the least squares method yielded the most selective analysis when four lines were used for four-components mixture, introduction of the component entropy yielded an increase in the selectivity level by measurement of six lines.