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

CO2 laser photoacoustic spectroscopy was used for quantitative analysis of a multicomponent gaseous mixture of pollutants with similar chemical struct ures (toluene, ortho-, patra- and meta-xylenes) in trace concentrations (50 -700 ppm). The agreement with the results of gravimetric measurements was b etter 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 squa res method was compared with a method based on the principle of calculation of the lowest component entropy. While the least squares method yielded th e most selective analysis when four lines were used for four-components mix ture, introduction of the component entropy yielded an increase in the sele ctivity level by measurement of six lines. (C) 2000 Elsevier Science B.V. A ll rights reserved.