Fundamental relationships in gas chromatography

The exact definition of the compressibility correction factor,j, has been extensively discussed in recent literature. In this work, it is shown that this compressibility correction factor has several different interpretations; however, the simplest and most useful meaning involves a correction from the experimentally accessible pressure at the outlet of a column to the average pressure in the column. Also, an unconventional definition of the retention volume of a solute in terms of the sample size and the equilibrium concentration of the solute in the mobile phase is presented. This retention volume definition is presented as an alternative to the common definition of V-R as the volume of carrier gas which passes through the column in a period of time called the retention time. In this discussion, it is emphasized that the temperature dependence of the specific retention volume is determined by the thermodynamics of the phase distribution process for the solute and not by an equation-of-state for the carrier gas. Finally, the conventional correction of the specific retention volume by a factor of 273/T-c can be used to correct a volume of carrier gas to a pseudo-standard state of 273 K and the average pressure in the column; however, this corrected specific retention volume has no relation to the specific retention volume that would be experimentally obtained at this standard state temperature and pressure.