3.1 This guide summarizes the test methods used in the elemental analysis of crude oils. Additional information on the significance and use of the test methods quoted in this guide can be found under discussion of individual test methods in Sections 8 through 15.

3.2 Crude oils are highly complex hydrocarbons also containing some organometallic compounds, inorganic sediment, and water. Nearly 600 individual hydrocarbons, over 200 separate sulfur compounds, and about 40 trace elements have been found in crude oils (1).6 Generally, sulfur and nitrogen are the two most abundant elements found in crude oils except for carbon and hydrogen. Most other inorganic elements are present at trace levels (mg/kg). Sulfur, nitrogen, vanadium, nickel, and iron are the most frequently determined elements in the crude oils. Ratios such as vanadium to vanadium + nickel, and iron to vanadium are suggested as being useful for oil type characterizations. Since organometallic compounds are concentrated in the heavy ends of petroleum, transition element concentrations and ratios can serve as excellent oil-oil correlation parameters. Generally, vanadium and nickel content increases with asphaltic content of crude oil (API gravity is an indicator). Lighter crude oils contain lesser amounts of metals (2, 3).

3.3 Metal complexes called porphyrins are a major component of metallic compounds in crude oils. The principal porphyrin complexes are Ni⁺² and VO⁺² compounds. There are also other non-porphyrin complexes and other metallic compounds present in crude oils (4, 5).

3.4 Some typical literature citations in this area are included in the reference section at the end of this guide.

1.1 This guide summarizes the current information about the test methods for elemental and associated analyses used in the analysis of crude oils. This information can be helpful in trade between the buyers and sellers of crude oil. Elemental analyses tests form an important part of quantifying the crude oil quality.

1.2 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.