Independent of local properties mathematical models for the calculation of retention indices in programmed temperature gas chromatography

Retention indices of some phthalates separated in temperature programming on SE-30 packed column were calculated by smoothing calibration data with Bezier curves, and from 2 to 6 order B-splines. The values thus obtained were compared to thr: corresponding ones calculated in a classical way. Whatever the standard n-alkane mixtures used (homologous series, alternate members with even or odd carbon atoms, any mixture with consecutive members not exceeding 4 carbon atoms between each two) the B-splines interpolations lead to retention indices values in better agreement with these ones, although Bezier curve smoothing still leads to values more consistent with the scheme of retention indices. Referring the phthalates to n-alkane standard mixtures, with consecutive members not exceeding 3 or 3 carbon atoms between each 2,, connecting the calibration data by B-splines, with orders from 2 to 5. and selecting the set of retention indices corresponding to the smallest value of the sum of squared second divided differences one may recover, with a good accuracy, classical programmed retention indices.