The retention index increment for the addition of a methylene group to the alkyl group of an analyte molecule is shown to be lower din 100 i.u. for N-substituted amino s-triazines. In temperature progammed gas chromatography, a linearly interpolated retention index I, determined from the linear regression equation, I=AZ+ (GRF)(z), with the number of atoms (Z) in the molecule as variable, was used to describe the retention of 25 N-substituted amino s-triazines, on DB-1, DB-5 and DB-WAX capillary columns, divided into five series according to the similarity of the alkyl groups in the particular, series. In the above equation, A is the linear regression coefficient or the retention index increment per atom addition, Z the number of C, N and Cl atoms in the molecule, and (GRF)(z) the group retention factor or functionality constant for functional groups in die molecule, based on the number Z. It is possible to estimate the retention indices of an unknown member of the series from the Z, A and (GRF) values.
