ASTM D7096 Standard Test Method for Determination of the Boiling Range Distribution of Gasoline by Wide-Bore Capillary Gas Chromatography
4. Summary of Test Method
4.1 The sample is vaporized and transported by carrier gas into a non-polar, wide-bore capillary gas chromatographic column. The column temperature is raised at a reproducible, linear rate so as to elute the hydrocarbon components in boiling point order for measurement by a flame ionization detector. Conditions are selected such that n-pentane and lighter saturated hydrocarbons in the calibration mixture are resolved discretely. Linear correlation between hydrocarbon boiling point and retention time is established using a known mixture of hydrocarbons covering the boiling range expected in the sample. Area slices are converted to volume using theoretical hydrocarbon volume response factors. Oxygenated samples require experimental determination of oxygenate response factors.
5. Significance and Use
5.1 The determination of the boiling range distribution of gasoline by gas chromatographic simulated distillation provides an insight into the composition of the components from which the gasoline has been blended. Knowledge ofthe boiling range distribution of gasoline blending components is useful for the control of refinery processes and for the blending of finished gasoline.
5.2 The determination of the boiling range distribution of light hydrocarbon mixtures by gas chromatographic simulated distillation has better precision than the conventional distillation by Test Method D86. Additionally, this test method provides more accurate and detailed information about the composition ofthe light ends. The distillation data produced by this test method are similar to that which would be obtained from a cryogenic, true boiling point (15 theoretical plates) distillation.
6. Interferences
6.1 Ethanol or other oxygenates may coelute with hydrocarbons present in the sample. Since the response of oxygenates is substantially different from the response of hydrocarbons, response factors are used to correct the area slice for the elution interval of oxygenates.
6.2 Concentrations of n-pentane and lighter saturated compounds may be estimated from the analysis. However, early eluting olefins present in the gasoline samples may coelute with these compounds.
6.3 For samples containing ethanol, this test method will determine the hydrocarbon distribution. It will not simulate the azeotrope observed during physical distillation.
