ASTM D6591-19

5.1 The aromatic hydrocarbon content of motor diesel fuel is a factor that can affect exhaust emissions and fuel combustion characteristics, as measured by cetane number.

5.2 The United States Environmental Protection Agency (US EPA) regulates the aromatic content of diesel fuels. California Air Resources Board (CARB) regulations place limits on the total aromatics content and polynuclear aromatic hydrocarbon content of motor diesel fuel, thus requiring an appropriate analytical determination to ensure compliance with the regulations.

5.3 This test method is applicable to materials in the same boiling range as motor diesel fuels and is unaffected by fuel coloration. Test Method D1319, which has been mandated by the US EPA for the determination of aromatics in motor diesel fuel, excludes materials with final boiling points greater than 315 °C (600 °F) from its scope. Test Method D2425 is applicable to the determination of both total aromatics and polynuclear aromatic hydrocarbons in diesel fuel, but is much more costly and time consuming to perform. Test Method D5186, currently specified by CARB, is also applicable to the determination of both total aromatics and polynuclear aromatic hydrocarbons in diesel fuel. Test Method D5186, however, specifies the use of supercritical fluid chromatography equipment that may not be readily available.

1.1 This test method covers a high performance liquid chromatographic test method for the determination of mono-aromatic, di-aromatic, tri+-aromatic, and polycyclic aromatic hydrocarbon contents in diesel fuels and petroleum distillates boiling in the range from 150 °C to 400 °C. The total aromatic content in % m/m is calculated from the sum of the corresponding individual aromatic hydrocarbon types.

1.2 The precision of this test method has been established for diesel fuels and their blending components, containing from 4 % to 40 % (m/m) mono-aromatic hydrocarbons, 0 % to 20 % (m/m) di-aromatic hydrocarbons, 0 % to 6 % (m/m) tri+-aromatic hydrocarbons, 0 % to 26 % (m/m) polycyclic aromatic hydrocarbons, and 4 % to 65 % (m/m) total aromatic hydrocarbons.

1.3 Compounds containing sulfur, nitrogen, and oxygen are possible interferents. Mono-alkenes do not interfere, but conjugated di- and poly-alkenes, if present, are possible interferents.

1.4 By convention, this standard defines the aromatic hydrocarbon types on the basis of their elution characteristics from the specified liquid chromatography column relative to model aromatic compounds. Quantification is by external calibration using a single aromatic compound, which may or may not be representative of the aromatics in the sample, for each aromatic hydrocarbon type. Alternative techniques and methods may classify and quantify individual aromatic hydrocarbon types differently.

1.5 Fatty Acid Methyl Esters (FAME), if present, interfere with tri+-aromatic hydrocarbons. If this method is used for diesel containing FAME, the amount of tri+-aromatics will be over estimated.

1.6 This test method includes a Relative Bias section for Test Method D6591 versus Test Method D1319 and Test Method D5186 versus Test Method D6591 for diesel fuels only. The applicable concentration ranges of the correlations are presented in the Relative Bias section. The correlations are applicable only in the stated ranges.

1.7 This test method and correlations were developed for diesel samples not containing biodiesel; the presence of biodiesel will interfere with the results. The correlation equations are only applicable between these concentration ranges and to diesel fuels that do not contain biodiesel.

1.8 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.