COMPARATIVE-STUDY OF DIFFERENT APPROACHES FOR THE FLOW-INJECTION FOURIER-TRANSFORM INFRARED DETERMINATION OF TOLUENE IN GASOLINES

A single channel flow injection manifold has been employed to carry out the direct determination of toluene in gasolines by FT-IR without any sample pretreatment and by using different strategies. Toluene can be directly determined by measuring the absorbance at 728 cm-1, using a base line established between 835 and 575 cm-1; and in this case a limit of detection of 0.01% (v/v) can be obtained with a dynamic range up to 2% (v/v). In some cases it could be convenient to determine toluene by derivative flow-injection FT-IR in order to avoid matrix interferences in the analysis of some types of gasolines. Carrying out the first order derivative FI-FT-IR measurements on the 728 cm-1 band between the peak at 731 and the valley at 725 cm-1 toluene can be determined without problems in establishing the base line and with a limit of detection of 0.01% (v/v). On the other hand, the use of the quotient between the first order derivative absorbance values of toluene, at the 728 cm-1 band, and benzene, at the 675 cm-1 band, can be applied for the determination of toluene in gasolines in which benzene has been previously analyzed, avoiding problems related to the determination of the base line and making measurements independent of the spacer employed.