The standard “ASTM D6729-20 Standard Test Method for Determination of Individual Components in Spark Ignition Engine Fuels by 100-Meter Capillary High Resolution Gas Chromatography” published by the American Society for Testing and Materials (ASTM) describes a test method for determining individual hydrocarbon components of spark-ignition engine fuels and blends containing oxygenate mixtures having boiling ranges up to 225 degrees.
Other light liquid hydrocarbon mixtures typically encountered in petroleum refining operations, such as blend stocks (naphthas, reformates, alkylates), can also be analyzed, but statistical data have been obtained only with blended spark-ignition engine fuels.
Based on collaborative study results, individual component concentrations and precision are determined over the range of 0,01 mass percent to approximately 30 mass percent. The procedure is applicable to higher and lower concentrations for individual components, however, the user should verify accuracy if the procedure is used for components with concentrations outside the specified ranges.
This test method also determines methanol, ethanol, t-butanol, methyl t-butyl ether, ethyl t-butyl ether, t-amyl methyl ether in spark-ignition engine fuels in the concentration range of 1 mass percent to 30 mass percent.
Although the majority of individual hydrocarbons present are identified, co-elution of some compounds is encountered. If this test method is used to estimate the bulk hydrocarbon group type composition, the user of such data should be cautioned that some errors will be encountered due to co-elution and not identifying all components present. Based on gasoline samples from an interlaboratory cooperative study, this procedure is applicable to samples containing less than 25 mass percent olefins. However, since analysis is based entirely on the retention times of the eluting components, caution should be exercised when analyzing samples that do not contain olefins using this test method, as some paraffins may be reported as olefins.
Total olefins in samples may be obtained or verified by other test methods described in ASTM D1319-19 or ASTM D6839-17, or both, if necessary.
If water is present or suspected to be present, its concentration can be determined, if desired, using the ASTM D1744-92 test method. Other compounds containing oxygen, sulfur, nitrogen, etc. may also be present and may co-elute with the hydrocarbons. If determination of these specific compounds is required, it is recommended that the test methods described in ASTM D4815-22 and ASTM D5599-18 for oxygenates and ASTM D5623-19 for sulfur compounds be used.
In applying the ASTM D6729-20 test method, representative samples of petroleum liquid are introduced into a gas chromatograph equipped with an open-tube (capillary) column coated with a specified stationary phase. The helium carrier gas passes the vaporized sample through the column, where it separates into individual components that are detected by a flame ionization detector as they elute from the end of the column. The detector signal is recorded digitally by an integrator or integrated computer. Each eluting component is identified by comparison with the retention time determined by analyzing reference standards or samples under the same conditions. The concentration of each component, in mass percent, is determined by normalization of the peak areas after correction for the selected components by detector response factors. Unknown components are reported separately and as a summary total.
Knowledge of the specified individual component composition (specification) of gasoline fuels and blendstocks is useful for refinery quality control and product specification. Process control and product specification compliance for many individual hydrocarbons can be determined by use of this test method.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides certification and testing services defined in the standard “ASTM D6729-20 Standard Test Method for Determination of Individual Components in Spark Ignition Engine Fuels by 100-Meter Capillary High Resolution Gas Chromatography” with its trained and expert staff and advanced technological equipment.
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