Threshold temperatures for solute mobility. Their determination and effect on programmed temperature gas chromatographic separations

Abstract

SummaryThe threshold temperature for solute mobility is defined as that temperature at which a solute band, which was initially cold trapped at the head of the column, begins moving through the column. It is shown that the separation of compounds by programmed temperature gas chromatography (PTGC) occurs primarily at the head of the column as a result of differences in threshold temperatures. Additional column length beyond that needed to trap the compounds improves resolution, primarily by delaying emergence (while maintaining the temperature and time spacing) thus allowing the column temperature to rise, the solute terminal velocities to increase, and narrower peak widths to be recorded. For maximum resolution in minimum analysis time, the initlal tempeiature must be at or below the threshold temperature of the most volatile compound in the mixture to be separated.Three methods for determining threshold temperatures are presented.

Fundamental Relationships of Chromatography

“…Saxton has proposed that the emergence temperature (elution temperature) in temperature programmed gas chromatography can be used as a physical constant in the same way that boiling point is used to identify individual solutes from tabulated reference data [168,169]. This approach assumes a model akin to extractive distillation in which solute retention times are the product of two distinct sequences.…”