5.1 These test methods cover the determination of total oxygen in gasoline and methanol fuels, and they complement Test Method D4815, which covers the determination of several specific oxygen-containing compounds in gasoline.

5.2 The presence of oxygen-containing compounds in gasoline can promote more complete combustion, which reduces carbon monoxide emissions. The Clean Air Act (1992) requires that gasoline sold within certain specified geographical areas contain a minimum percent of oxygen by mass (presently 2.7 % by mass) during certain portions of the year. The requirement can be met by blending compounds such as methyl tertiary butyl ether, ethyl tertiary butyl ether, and ethanol into the gasoline. These test methods cover the quantitative determination of total oxygen which is the regulated parameter.

5.2.1 Only seven U.S. states have such wintertime requirements, and others with EPA approval have opted out of the program. The minimum oxygen limit now varies from 1.8 % to 3.5 % by mass. For methanol/heavier alcohol blend EPA waivers, the maximum oxygen content allowed is 3.5 % or 3.7 % by mass.

5.2.1.1 Only ethanol is used for such blending in the U.S. Ethers are banned by some states and are not used in all states because of water contamination issues.

1.1 These test methods cover the quantitative determination of total oxygen in gasoline and methanol fuels by reductive pyrolysis.

1.2 Precision data are provided for 1.0 % to 5.0 % oxygen by mass  in gasoline and for 40 % to 50 % oxygen by mass  in methanol fuels.

1.3 Several types of instruments can be satisfactory for these test methods. Instruments can differ in the way that the oxygen-containing species is detected and quantitated. However, these test methods are similar in that the fuel is pyrolyzed in a carbon-rich environment.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 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.

1.6 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.