Simultaneous determination of Solvent Yellow 124 and Solvent Red 19 in diesel oil using fluorescence spectroscopy and chemometrics.

Differences in tax levels for diesel oil stimulate the illegal removal of characteristic diazo compounds purposely added to designate its possible usage. In order to reduce the losses in the national income, there is a strong need to develop a sensitive and cost-effective analytical procedure for the detection of this illegal action. In this study, we describe a novel analytical approach for a qualitative and quantitative determination of two diazo compounds (Solvent Yellow 124 and Solvent Red 19) that are usually added to diesel oil. The methodology proposed combines the use of excitation-emission matrix fluorescence spectroscopy as an analytical technique and partial least squares regression as a multiple modeling tool. With this new methodology, relatively low root mean square errors of prediction (for independent set of test samples) that are equal to 0.223 for Solvent Red 19 and 0.263 for Solvent Yellow 124, were obtained and the results were stable, which were indicated by an analysis performed after 48 and 96 h. The methodology is also nondestructive and allows for (i) simultaneous detection of diesel oil additives, (ii) determination of satisfactory limits of detection (0.048 and 0.042 mg L(-1) for Solvent Red 19 and Solvent Yellow 124, respectively), and (iii) obtaining of considerably low relative standard deviations of 2.33% for Solvent Yellow 124 and of 3.23% for Solvent Red 19 in comparison with the existing norm level.