James-Martin correction factor

If the mobile phase is a liquid, and can be considered incompressible, then the volume of the mobile phase eluted from the column, between the injection and the peak maximum, can be easily obtained from the product of the flow rate and the retention time. For more precise measurements, the volume of eluent can be directly measured volumetrically by means of a burette or other suitable volume measuring vessel that is placed at the end of the column. If the mobile phase is compressible, however, the volume of mobile phase that passes through the column, measured at the exit, will no longer represent the true retention volume, as the volume flow will increase continuously along the column as the pressure falls. This problem was solved by James and Martin [3], who derived a correction factor that allowed the actual retention volume to be calculated from the retention volume measured at the column outlet at atmospheric pressure, and a function of the inlet/outlet pressure ratio. This correction factor can be derived as follows. 

The following table provides the Martin-James compressibility factor, j,1 and the Giddings plate height correction factor, f,2 for chromatographically useful pressures. These quantities are defined as... 

Martin-James Compressibility Factor and Giddings Plate Height Correction Factor... 

Figure 10.5. Plot of James-Martin pressure-gradient correction factor / as a function of the compression ratio P = pjp0 for a GC column.

Where j is the James-Martin pressure-gradient correction factor... 

Prove that the James-Martin pressure-gradient correction factor j approaches zero as P- oo and approaches unity as 1. Deduce these limits on a physical basis using the result j = u/v0. 

James-Martin pressure correction factor (compressibility factor)... 

In both cases, the James-Martin factor for the correction of gas compressibility under pressure difference between column inlet, pi, and column outlet, po, is introduced ... 

The net retention volume V, corrected for the pressure drop across the column by the gas compressibility factor of James and Martin (20) Is given by... 

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