Express analyzers of motor fuels: the problems of metrological support

The problems of identifying counterfeit motor fuels in real conditions are highlighted. It is noted that the use of express analyzers of motor fuels does not provide the necessary level of control over the accuracy and reliability of the results of measuring parameters of the fuel under study. The metrological support of express analyzers, the operating principle of which is based on the method of near-infrared spectroscopy, is considered. This method rejects the classical spectroscopic approaches in favor of complex multidimensional mathematical models. As a result, the analytical result becomes a forecast, since the quantitative analysis is replaced by a new form of qualitative analysis; the conventional metrological approaches become inapplicable; the category of uncertainty is replaced with a much less developed category of reliability; and typical procedures and means of accuracy control become insufficient. An approach to evaluation of metrological characteristics of express analyzers of motor fuels is proposed in case when the mathematical model for calculating the analyzed parameters cannot be accessed, since it is an intellectual property of the analyzer developers. Such approach will help determine the relevance of the express analyzer built-in model for specific grades of motor fuels. Domestic express analyzers have been studied, the measurement principles of which are based on dielectric permeability of fuels. For express analyzers based on the principles of dielectrometry and near-infrared spectroscopy, the identification of counterfeit fuel turned out to be approximately the same: an addition of 8–10 vol. % of the counterfeit component practically does not change the measurement results. Due to inability to study the original mathematical model utilized in the express analyzer software, alternative methods of evaluating the reliability of the analytical results, based on simplified models created for fuels with various added components and additives, have been proposed. It was shown that such additives make it possible to evaluate the calibration quality related to a specific component. A method has been developed to enable the evaluation of sensitivity of various types of express analyzers to unauthorized additives (variants of the addition method), which are used in the manufacturing of counterfeit motor fuels. The proposed variants of the addition method are recommended for monitoring the reliability of the results of express fuel analysis.