【国外标准】 Standard Test Method for Separation and Determination of Aromatics, Nonaromatics, and FAME Fractions in Middle Distillates by Solid-Phase Extraction and Gas Chromatography

5.1 For the middle distillates whose boiling range is between 170 °C and 400 °C by such distillation methods like Test Method D2887, Procedure A can separate and determine the content of total aromatics and total nonaromatics by SPE and GC analysis of the resulting fractions. The determination of the total content of saturates and aromatics in petroleum middle distillates is useful to investigate the effects of petroleum processes on production of various finished fuels.5.2 The total aromatics content and polycyclic aromatics content are important to characterize the quality of diesel fuels. This test method is demonstrated to be time-saving and eco-friendly by reducing the amount of reagent consumption and avoiding the necessity of solvent evaporation step as required, for example, in such Test Method D2549.5.3 The determination of detailed hydrocarbon composition by mass spectrometry requires a preliminary separation of the sample into representative aromatics and nonaromatics, as in Test Method D2425, where Test Method D2549 is used to separate the distillate fuel. The SPE fractionation procedure described herein may provide a suitable fractionation alternative approach for these mass spectrometric types of methods.5.4 Biodiesel is a blendstock commodity primarily used as a value-added blending component with diesel fuel. Procedure B can provide a separation and determination technique to monitor the FAME content for FAME biodiesel blends.1.1 This test method covers the separation and determination of representative aromatics, nonaromatics, and fatty acid methyl ester (FAME) fractions in middle distillates that boil between 170 °C and 400 °C, including biodiesel blends with up to 20 % by volume of FAME, by solid phase extraction and gas chromatography.1.2 This test method provides two procedures, A and B. Procedure A is applicable to the petroleum-based middle distillates fuel, and Procedure B is applicable to the biodiesel blends with up to 20 % by volume of FAME.1.3 This test method is applicable to middle distillates samples with aromatics content ranging from 5 % to 50 % by mass and biodiesel blends with FAME content in the range of 0.5 % to 20 % by volume. This test method may apply to concentrations outside these ranges, but the precision has not been determined.1.4 For Procedure B, biodiesels in the form of fatty acid ethyl ester (FAEE) can also fully elute into the FAME fraction, and they have the similar FID (flame ionization detector) relative response factors with that of FAME. The determined content of FAME fractions are the sum of concentrations of FAME and FAEE by this test method (see 3.2.5).1.5 From the investigation results obtained for FAME determination, the low concentrations of monoglycerides (usually less than 0.5 % by mass in biodiesel blends) are not detectable under the gas chromatographic (GC) condition of this test method and will not interfere with the determination of FAME by Procedure B. As a result, biodiesel blends, conforming to the requirements of Specification D7467, containing up to 20 % by volume of biodiesel blendstock meeting the requirements in Specification D6751, typically contain concentrations of monoglycerides of less than 0.1 % by mass. The diglycerides and triglycerides, if present, are not detected under the GC condition of this test method due to their higher boiling points.NOTE 1: If a sample is suspected of containing an abnormal FAME biodiesel feedstock than specified in Specification D6751, for example, a sample contaminated with vegetable oil with a high level of total triglycerides, the content of mono-, di-, or tri-glycerides in the isolated FAME fraction may be determined using Test Method D6584. Samples containing biodiesels with a high amount of glycerides than specified in Specification D6751 may contaminate the GC column and not recommended for this test method.1.6 The values stated in acceptable SI units are to be regarded as the standard. No other units of measurement are included in this standard1.7 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.1.8 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.