REPORT FOR ANALYTICAL CHEMISTS
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ANALYTICAL CHEMISTRY
The big advantage of the reten tion index system is that the values given in this form are descriptive. For example, if the retention index of a substance on a particular col umn is 930, this value immediately shows that it will emerge some where after n-nonane. Similar to the usual retention values, the retention indices are also dependent on the chemical na ture of the stationary phase and the temperature. Thus, for better un derstanding of this concept, the cor relations between the retention in dex and the temperature and sta tionary phase have to be investi gated.
The difference between two reten tion indices determined on one sta tionary phase is termed as u / ; this can express either the difference of the retention indices of one sub stance measured at two tempera tures (dT/dT) or the difference of the retention indices of two sub stances determined at the same tem perature. When the retention index of a particular substance is determined on two different stationary phases but at the same temperature, the difference between the two values is indicated as^I. TEMPERATURE DEPENDENCY ON THE RETENTION INDEX
NOMENCLATURE
The retention index is expressed by the symbol I. By convention, the temperature at which the meas urement was made is given in sub script with the stationary phase as superscript. Thus, for example, a retention index determined at 130° C. on squalane stationary phase is characterized as Γ*™ίαη\
It is known that the relationship between the logarithms of the net retention volumes or the adjusted retention times and the reciprocal of the absolute column temperature is linear. On the other hand, the retention index values are directly proportional to the column temper ature and in first approximation, this correlation is linear although—
