Development of a WD-XRF analysis method of minor and trace elements in liquid petroleum products

Abstract

This paper describes a methodology for the analysis of minor and trace elements in liquid petroleum products, with varying oxygen content between 0% w/w and 3.4% w/w and varying C/H ratio between 7 and 9, by wavelength-dispersive X-ray fluorescence (WD-XRF) spectrometry, necessary to determine the properties that indicate the function and performance of the product in service.

There are a number of standard methods of chemical analysis by WD-XRF, atomic absorption spectrophotometry (AAS) or inductively coupled plasma atomic emission spectrometry (ICP-OES) that apply to one type of petroleum product. However, there is not a standard that applies to any kind of liquid petroleum products in a huge range of concentrations with low detection limits and uncertainties, that allow to control a great number of products in a huge range of concentrations of an elevate number of elements.

In order to obtained a rapid an accurate methodology that allows the analysis of different materials in a huge range of concentrations, a WD-XRF method of measuring a set of elements: Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, S, Si, Ti, V and Zn, in a series of liquid petroleum products was developed being fine-tuned by optimising the measurement conditions and calculating the detection and quantification limits. The validation was carried out by using a series of reference materials and the uncertainty of the method was calculated.

The analysis of sulphur was also performed by elemental analysis in addition to WD-XRF and the results obtained by both techniques were compared. The matrix of the different samples analysed and the standards used was also analysed by determining C, H, N and O.