DIRECT DETERMINATION OF BENZENE IN GASOLINE BY FLOW-INJECTION FOURIER-TRANSFORM INFRARED SPECTROMETRY

A Fourier transform infrared spectrometric procedure for the automated determination of benzene in gasoline was developed, based on the use of flow-injection analysis. The method permits the direct determination of benzene without any pretreatment of samples, with a limit of detection of 0.02% (v/v) and a relative standard deviation of ca. 1% [for five independent analyses of a diluted sample containing a 0.4% (v/v) of benzene]. Results found by direct analysis agreed with those obtained by off-line and on-line standard addition methods. A rapid quality control procedure was developed, based on the on-line injection of gasoline samples (diluted 1 + 9 in hexane) into a carrier stream of a 0.5% (v/v) solution of benzene in hexane; in this instance, the baseline corresponds to the upper limit tolerated by the European Economic Community's law for gasolines. Thus, the injection of diluted samples with an appropriate level of benzene must provide no peaks or negative peaks, whereas those with a benzene concentration higher than that tolerated provide positive peaks. A series of real samples were analysed by the proposed procedure and the results obtained were comparable to those given by gas chromatography.