Experimental study of the effect of column length and pressure on the hetp in gas chromatography

Abstract

HETP vs. carrier gas velocity curves were measured on columns of different lengths operated under laminar flow conditions at either a constant outlet or a constant inlet column pressure, as well as on columns of a given length operated at various levels of the outlet or the inlet column pressure, respectively. Both high and low amounts of liquid stationary phase on the support were employed. With columns operated at a constant outlet pressure, the minima on the curves were shifted towards lower HETP and flow velocity values and the ascending branches of the curves acquired a more dished curvature upon increase of column length. The reverse situation was encountered with columns operated at a constant inlet pressure. An increase in the mean absolute column pressure brought about by an increase of either the outlet or the inlet column pressure always resulted in a pronounced decrease of the minimum HETP and optimum velocity, as well as in a steeper and straighter ascending branch of the HETP vs. velocity curve when working with the high liquid load packing; with a low loading of liquid stationary phase an inappreciable decrease of the minimum HETP occurred under the above conditions. Disagreements between the present results and those obtained by other authors are discussed.