Computer-assisted prediction of gas chromatographic separations

Abstract

A computer program is presented which allows the prediction of gas-liquid chromatographic retention behavior, and, thus, the separation of complex mixtures, with binary stationary phases. The method is based upon the law of diachoric solutions, ▪ where K R is the liquid-gas partition coefficient for a solute with a stationary phase composed of a mixture of A and S of volume fractions, ⊘ A and ⊘ S , respectively; K R( A) and K R( S) are the solute partition coefficients for pure A and pure S. Computerdrawn plots of K R vs. ⊘ A and a vs. ⊘ A are used to find the optimum A + S composition which will separate a given mixture, and, in addition, predict the a value for the two most difficult solute pairs at that point. This enables the column length necessary for the baseline separation of all components to be calculated. With certain limitations, relative retention times and weight fractions, rather than partition coefficients and volume fractions, can be employed. In the examples given, a 5-component steroid mixture and a 40-component hydrocarbon mixture are virtually completely separated by the computer-assisted application of the described procedure. The only limitations to the method appear to be the turn-around time of the computer installation, and the accuracy of the K R and ⊘ A data.