The additivity concept in the retention index system of Kovats has been examined for a series ofn-alkylbenzenes and theiro- andp-monosubstituted nitro-, amino-, and chloro-derivatives. Anomalous behaviour is exhibited by the first three members of the series on both polar and non-polar stationary phases. For addition of a methylene group ton-propylbenzene or ap-substituted derivative, it is found that the retention increment, Δl CH2, approaches 100 units. However, the strong inductive effect of the group in the ortho position and the steric effects apparent in ano-substituted alkylbenzene lead to large variations of retention increment upon addition of-CH2-to the alkyl chain.
A study ofn-alkylbenzene retention on Apiezon L and Carbowax 20M over a wide range of temperatures has verified the linearity of the retention increment with temperature and has revealed that this gradient increases with increasing carbon side-chain length for the first few members of the series, thereafter becoming constant. Functional retention increments, Δlx, for substitution of nitro-, amino- and chloro-groups into the benzene ring are given.
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Dedicated to Dr. E. Kováts on the occasion of the 25-year anniversary of his invention of the retention index system.
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Vernon, F., Suratman, J.B. The retention index system applied to alkylbenzenes and monosubstituted derivatives. Chromatographia 17, 600–604 (1983). https://doi.org/10.1007/BF02261943
- Gas chromatography
- Retention index
- Alkyl benzenes