Agc instrument was operated in the isothermal mode (constant t) to determine retention indices. adjusted retention times (tr-tm) values of 2.21, 7.61 and 25.11 min were obtained for n-butane, n-hexane and n-octane, respectively. the compounds 2-butene, n-propanol and toluene gave adjusted retention times of 2.67, 7.60 and 16.32 min, respectively. calculate the retention indices for these three compounds.