Comparison and Critical Evaluation of Analytical Performance of Wavelength Dispersive X-ray Fluorescence and Ultraviolet Fluorescence for Sulfur Determination in Modern Automotive Fuels, Biofuels, and Biocomponents

Abstract

The significant decrease of admissible sulfur content, wide implementation of variety of components of biological origin and adequate changes of additives packages create new challenges in terms of S determination in modern automotive fuels. Wavelength dispersive X-ray fluorescence spectrometry (WD XRF) and ultraviolet fluorescence spectrometry (UVF) are currently the obligatory methods for the determination. Both methods fulfill requirements of detection and precision (much better performance of UVF) as well as give successful results in certified reference materials analysis, proficiency testing, and intermethod comparisons. Apart from satisfactory results for good quality fuels, some difficulties can be met in crucial cases, when S admissible content is exceeded. S content can be apparently exceeded in UVF analysis due to nitrogen interference as well as apparently not exceeded in UVF, and apparently not exceeded (filtered sample) or apparently exceeded (sediment on the bottom) in WD XRF analysis in cases of inhomogenous fuel samples containing S in the solid phase. In such cases, the mandatory methods will not reveal (UVF) or will not be able to prove quantitatively (WD XRF) the contamination of automotive fuels. The work shows that the system of automotive fuels quality assessment needs improvement in terms of S content control. Simplified standard addition method turned out to be efficient for overcoming multiplicative effect of absorption by main components of matrix (C, H, and O) in WD XRF, but it does not correct N influence on UVF determination that is an effect of additive character.