Multidimensional Surface and Constant Average Column Pressure van Deemter Plots: Two New Conceptual Tools for Gas Chromatography

The graphic representation of the effect of mobile phase flow rate or velocity on column efficiency is a commonly used tool for optimizing GC column performance. Such plots are referred to as van Deemter plots. In addition, van Deemter equation coefficients have been used to derive fundamental values such as gas phase diffusion coefficients. Since a GC column is usually operated at a fixed outlet pressure (typically atmospheric pressure), the role of average column pressure as a variable in the van Deemter equation, separate from mobile phase velocity, is usually not considered. Investigations into the technique of vacuum outlet gas chromatography have recently led to an exploration of such a relationship. In these investigations, two new concepts have proven to be useful tools. Multidimensional van Deemter surface plots are an aid to understanding the relationship between mobile phase velocity, column pressure, and column efficiency. Constant average column pressure van Deemter plots may facilitate the determination of values of the van Deemter equation coefficients that are more useful for deriving accurate fundamental values.