Theory of Minimum Time Operation in Gas Chromatography

Abstract

The theory of minimum analysis time for packed and capillary columns is developed with particular emphasis on the role of the column pressure drop. Using a previously derived equation for the effect of pressure gradients on plate height, this analysis shows that the column outlet should be held under vacuum for optimum performance. The column inlet should be maintained somewhat higher than the critical pressure, pc the inlet pressure below which a separation can never be obtained. Using optimum inlet and vacuum outlet pressure, the best carrier gas is found as that with the largest diffusivity to viscosity ratio. In the order of decreasing desirability one obtains H2, He, N2, CO2, and Ar. In addition, the theory is used to obtain the optimum thickness of the liquid layer in capillary columns. It is found that the capacity factor, k, directly related to thickness, is variable, being sometimes less than unity. © 1962, American Chemical Society. All rights reserved.