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.