Application of p-xylenesulphonic acid as ashing reagent in the determination of trace metals in crude oil

The p-xylenesulphonic acid ashing procedure was applied to the determination of Ca, Cu, Fe, Mg, Na, Ni and Zn in crude petroleum. The optimum acid ratio was 1.0 g per gram of oil for determining Na and Ni and 0.5 g per gram of oil for the other metals determined. The simultaneous ignition of the oil-acid mixture while boiling prevented volatilization losses for Fe, Na and Ni, eliminated the coke residue and reduced the ashing time. The minimum sample size for efficient metal release was 15.0 g. Satisfactory recoveries of added Na and Ni and highly reproducible results were obtained. Results obtained by this method were similar to those obtained by standard methods for the same samples.