Determining the concentration of vanadyl porphyrin in a sample of oil residue fractions above 360oC is carried out by using two standards- the primary and the secondary. The primary standard used in the experiment consist of a sample of vanadium sulfate (VOSO4*H2O) of known concentration, for determining the content of vanadyl complex in the oil, and the secondary standard consist of carbonized sugar for determining the content of the free radicals in the oil samples. The absolute concentration of the paramagnetic species is based on the total content of the vanadyl porphyrin and by comparing it with the primary standard then dividing it by the concentration of the secondary standard and by the amplitude of rubin sample. The EPR spectral form, for the residue oil samples are found to be uniform for all (that is fro both treated or non- treated samples), except the variation in the VO+2 concentration. The method further reveals that the VO+2 ions are present in matrix with other micro element forming the paramagnetic species in the residue oil fraction and this is responsible for its EPR spectral broad line. Other method of determining the concentration of VO+2 in oil i.e. method of atomic absorption spectroscopy is found to have a direct correlation with the method of EPR-spectroscopy by results.
