Logarithm-adjusted retention time carbon number plot

In practice, the retention index is simply derived from a plot of the logarithm of the adjusted retention time versus carbon number times 100 (Figure 4.4). To obtain a retention index, the compound of interest and at least three hydrocarbon standards are injected onto the column. At least one of the hydrocarbons must elute before the compound of interest and at least one must elute after it. A plot of the logarithm of the adjusted retention time versus the Kovats index is constructed from the hydrocarbon data. The logarithm of the adjusted retention time of the unknown is calculated and the Kovats index determined from the curve (Figure 4.4). 

It has lung been known that within a homologous series, a plot of the logarithm of adjusted retention time r = r the number of carbon atoms is lin-... 

It has long been known that within a homologous series, a plot of the logarithm of adjusted retention time (carbon atoms is linear, provided the lowest member of the series is excluded. Such a plot for C4 to C9 normal alkane standards is shown in Figure 27-18. Also indicated on the ordinate are log adjusted retention times for three compounds on the same column and at the same temperature. Their retention indexes are then obtained by multiplying the corresponding abscissa values by 100. Thus, the retention index for toluene is 749, and for benzene it is 644. 

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