Development of Crude Oil Reference Material Certified for the Concentrations of Sulfur, Iron, Nickel, Vanadium and Magnesium

Crude oil quality and uses are largely affected by the presence of sulfur and some other elements. Controlling the risk associated with these elements in crude oil depends on their accurate determination which is crucially governed by the use of certified reference materials (CRMs). This paper describes the development of a natural-matrix reference material for quantification of sulfur, iron, nickel, vanadium and magnesium in crude oil. The crude oil was homogenized and bottled to prepare the candidate material. Homogeneity and stability of the prepared reference material were investigated and characterization of sulfur content was carried out using wavelength-dispersive X-ray fluorescence (WD-XRF) spectrometry and gravimetric methods. Meanwhile, characterization of iron, nickel, vanadium and magnesium content was carried out using atomic absorption spectrometry (AAS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) techniques. Statistical evaluation of the data showed good homogeneity and stability of the candidate reference material. Sufficiently good agreement between methods of characterization was achieved which allowed certification. The certified values and their associated uncertainties were statistically derived using the approach of combining data from two or more independent analytical methods developed by National Institute for Standards and Technology (NIST, Gaithersburg, USA).