EXPLANATION
When fuels are combusted, metals present in the fuels can form low forming compounds corrosive to metal parts. Trace metals present in petroleum can deactivate catalysts during processing. These test methods cover the determination of nickel, vanadium, iron, and sodium in crude oils and residual fuels by flame atomic absorption spectrometry.
TEST SUMMARY
Two test methods are available. In Test Method A, the sample is decomposed with sulfuric acid. The residue is digested further with nitric acid, and diluted to volume with dilute nitric acid containing interference suppressant. The metals in the solution are determined by AAS using aqueous matrix matched calibration standards. A nitrous oxide-acetylene flame is used for vanadium, and an air-acetylene flame is used for nickel and iron.
In Test Method B, the sample is diluted with an organic solvent. Interference suppressant is added to the solution if vanadium is to be determined. A nitrous oxide-acetylene flame is used for vanadium, and an air-acetylene flame for nickel and sodium. Oil-soluble metal calibration standards are used. This test method does not purport to quantitatively determine nor detect insoluble particulates.
TEST PRECISION
Where X is the mean concentration in mg/kg.
Based on the NIST sample analysis, this test method has no bias for vanadium and nickel in Test Method A and for vanadium in Test Method B. However, nickel, in Test Method B shows a high bias. Bias for iron and sodium is not known.