ASTM D5599 Determination of Oxygenates in Gasoline
ASTM D5599 Standard Test Method for Determination of Oxygenates in Gasoline by Gas Chromatography and Oxygen Selective Flame Ionization Detection
4. Summary of Test Method
4.1 An internal standard of a noninterfering oxygenate, for example, 1,2-dimethoxyethane (ethylene glycol dimethyl ether) is added in quantitative proportion to the gasoline sample. A representative aliquot of the sample and internal standard is injected into a gas chromatograph equipped with a capillary column operated to ensure separation of the oxygenates. Hydrocarbons and oxygenates are eluted from the column, but only oxygenates are detected with the oxygen-selective flame ionization detector (OFID). A discussion of this detector is presented in Section 6.
4.2 Calibration mixtures are used for determining the retention times and relative mass response factors of the oxygenates of interest. Suggested calibrant materials are listed in 8.2.
4.3 The peak area of each oxygenate in the gasoline is measured relative to the peak area of the internal standard. A quadratic least-squares fit of the calibrated data of each oxygenate is applied and the concentration of each oxygenate calculated.
NOTE 1 - While 1,2-dimethoxyethane has been found to be an appropriate internal standard, other oxygenates may be used provided they are not present in the sample and do not interfere with any compound of interest.
5. Significance and Use
5.1 In gasoline blending, the determination of organic oxygenated compounds is important. Alcohols, ethers, and other oxygenates are added to gasoline to increase the octane number and to reduce tailpipe emissions of carbon monoxide. They must be added in the proper concentration and ratios to meet regulatory limitations and to avoid phase separation and problems with engine performance or efficiency.
5.2 This test method provides sufficient oxygen-to-hydro-carbon selectivity and sensitivity to allow determination of oxygenates in gasoline samples without interference from the bulk hydrocarbon matrix.
