1.1 This test method covers and provides for the analysis of high-purity (greater than 99.5 % by volume) n -heptane and isooctane (2,2,4-trimethylpentane), which are used as primary reference standards in determining the octane number of a fuel. Individual compounds present in concentrations of less than 0.01 % can be detected. Columns specified by this test method may not allow separation of all impurities in reference fuels. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.