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Behaviour of stationary phases. I. Linear relationships between retention data of benzene derivatives Retention times of about 140 benzenic mono- and polysubstituted compounds have been determined on a collection of stationary phases under isothermic conditions. The “numerical taxonomic aggregation” methods applied to these data lead to a classification of the stationary phases, in accordance with a measure of association between pairs of variables and an amalgamation rule for clustering. Three classes of phases (polar, non-polar and polyfluorinated) appear on the dendogram. Using the retention data relative to two phases, ϕ 1 and ϕ 2 , we show that a linear relationship between the two series of data is obtained whenever the two phases belong to the same cluster. This relationship (where coefficients a and b are constant in relation to Z, but vary with φ, ϕ 1 , ϕ 2 and T ) constitutes a general model, applicable to all benzenic compounds (mono-, di- or trisubstituted) under examination. The diversity of experimental conditions in the determination of retention data led us to a general updating of the various ways of expressing the retention, by simultaneously studying the effects of the temperature T and/or those of the nature of the stationary phase ϕ. We obtain a linear relationship in which Gr 1 and Gr 2 are either retention indexes, retention volumes or retention times, and Sq represents any carbon skeleton bearing the function Z. Such a relationship permits the comparison of interlaboratories results. Thus, although the characteristics of the columns and the experimental conditions vary, we obtain very satisfactory linear relationships between our own data expressed as log (reduced time) and those from the literature expressed either as indices or as log (retention volume) for stationary phases belonging to the same taxonomic class.

In chromatographic studies polar effect constants σ*c, similar to those of Taft and Ingold, can be obtained from an empirical additivity relationship which takes into account three structural increments.

Chromatographic behaviour of stationary phases. II. Application of factor analysis A “principal component analysis” applied to a set of retention times of 17 benzenic monosubstituted compounds on a collection of 21 stationary phases, leads to the following relationship: Knowing the experimental data , and of any substance P, measured on three phases, o 1 , o 2 and o 3 (respectively non-polar, polyfluorinated and polar) one can estimate the gas—liquid chromatographic retention data , of the same substance P on any stationary phase o i with the aid of the above relationship ( a o , b o , c o , and d o are the coefficients of the non-restricted multiparametric relationship.)

lComparison of stationary-phase classification scales Comparison of the stationary-phase classifications demonstrates their relation to the nature of the forces interacting between the solvent and the solute. The ?* factor, which expresses the intensity of the chromatographic interaction, seems to be the most satisfactory basis for classification at present.

Behaviour of ethers. VII. Principle of determination of the polar effect constants It is pointed out that the simplified linear extrathermodynamic relationship where retention data are plotted versus the polar factor and the number of ramifications located on the first carbon atom neighbouring the chemical function, leads to a satisfactory result. This relationship may be used for enlargement of the σ* scale, when applied to chromatographic phenomena. On the other hand, enlargement of this scale can be carried out by incrementation.

Behaviour of ethers. I. Working out a “Taft”-like equation founded on retention data of saturated ethers Variations in retention data of a series of saturated aliphatic ethers have been studied with a view to express them in a Taft-like equation. The linear relationships pointed out show the influence of the ramifications located on the atom neighbouring the oxygen. The numerical values of ϱ * are determined for six stationary phases. They express the selectivity of the stationary phases towards the ethers and they can be considered as an evaluation of the polarity of these substances.

L'etude de la variation du logarithme du temps de retention reduit relatif d'une serie d'allyloxyalcanes et de phenoxyalcanes est abordee a l'aide de la methode de topologie-information DARC, de sorte que les relations types obtenues tinnent compte de la contribution de chacun des atomes de carbone des groupements alkyles variables. De plus, ces relations elargissent le domaine de validite de la loi de James-Martin aux molecules ramifiees.

Application of a Taft-type equation to retention data. Additivity of substituent effects The previously established linear extrathermodynamic relationship can be applied to a chemical population the common functional group of which is characterized by an axis of symmetry. In all other cases it is possible to differentiate the particular contribution of each alkyl group Rl; consequently their effects must then be considered separately.

With the final aim of predicting chromatographic retention data, a population of mono- and poly-functional benzenes was subjected to diverse methods of multivariate analysis. Numerical taxonomic aggregation indicated three clusters of stationary phases, the polyfluorinated ones behaving very differently from the polar or non-polar phases Factor analysis was largely successful for the g.l.c. data prediction; the method is based on a multiparametric regression model.

Satisfactory reproduction of the retention data matrix in the case of a series of mono-substituted benzenes and a series of aliphatic substances proves the general character of the prediction equation where x Q i , φ j are the retention data x of unknown solute Q i on phase φ j ; a Q i , b Q i , c Q i and d Q i are regression coefficients which to some extent account for forces of orientation, charge transfer and association; and x ST i , φ j are independent variables representing the retention data of the four compounds of the standard set of substances on a given phase φ j . These four compounds are selected by diverse methods of multivariate analysis. The predicted values show very satisfactory agreement with the observed values.

In order to predict retention data in gas-liquid chromatography, extension of the Taft scale of σ * polar effect constants is essential and can be carried out by means of the equation log t ′ R = ρ * σ * + h ( n H -3). Using retention data of alcohols, σ * of 42 substituents have been estimated, giving rise to a σ * c scale appropriated in the field of chromatography.