Determination of kerosene as an adulterant in diesel through chromatography and high-resolution mass spectrometry

Abstract

In India, adulteration of petroleum-based automotive fuels is a serious concern which has attracted the attention of media and regulators from time to time. Monitoring adulteration of automotive fuels is often challenging due to the similarity in the properties of adulterants with that of the fuel (gasoline or diesel). The present study investigates a typically prevalent case of Euro IV diesel fuel adulteration with low-value subsidized kerosene. Diesel samples contaminated with kerosene were analyzed for density, viscosity, atmospheric distillation, aniline point, total sulfur and cetane index to generate an initial assessment of the adulteration. In view of the inadequacy of these methods in identifying the diesel adulteration even with up to 40% kerosene, chromatographic [gas chromatography (GC) and high-performance liquid chromatography (HPLC)] and high-resolution mass spectrometric (HRMS) analysis were carried out to detect the fingerprint regions in samples. Total sulphur, aniline point and atmospheric distillation (recovery at 250 °C) gives primary evidence for determining the presence of kerosene (adulterant) in diesel fuel. There was a considerable increase in the n-C10 to n-C12 and decrease in n-C15 to n-C20 hydrocarbons in the adulterated samples through GC. Similarly, the HRMS measurements showed a significant increase of alkylbenzenes concentration in the adulterated samples. A good correlation was observed between HPLC and HRMS results of saturates, mono, di, tri+-aromatics in adulterated diesel samples. The Student’s t test showed an excellent correlation between the values of different hydrocarbon groups in all the samples obtained with HPLC and HRMS analysis.