Resolution, Separability, and Conditions for Fraction Collection in Preparative Gas Chromatography

Abstract

The problem of resolution of neighboring chromatographic peaks has been mathematically re-examined with respect to the uses of gas chromatography as a tool for component purification and preparation, as well as for separation for quantitative analysis of mixtures. It has been found possible to deduce generally valid expressions and to develop charts to facilitate the computation of the number of plates required to give a desired fractional recovery of a sample component at a desired fractional impurity level for two components of specified relative volatility and weight ratio. The same methods also make possible the selection of cut points for component trapping to give specified fractional impurity levels when only a specified number of plates is available. The fractional recovery of the sample component possible at the required fractional impurity level is also furnished in this case. The results and implications of the new method are discussed in relation to the recovery index and separation efficiency of Glueckauf. The limitations of approximate equations existing in the literature for the number of plates required at a particular resolution R and relative volatility α are pointed out. When these equations are compared with the correct equations, it is seen that the approximate equations are not simpler than the correct ones to a degree that justifies their use, even at small values of the relative volatility where they approach the correct equations.