Pressure gradient correction

Net retention volume. VN- The adjusted retention volume multiplied by the pressure gradient correction factor. 

Pressure gradient correction factor. j. The factor that... 

Since a finite pressure drop exists over the length of the column, the adjusted retention volume is often multiplied by the pressure gradient correction factor, j, to give a net retention volume, VN. 

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. 

Prove that the pressure-gradient correction term fx from Eq. 12.20 approaches unity as P - 1 and approaches 9/8 as... 

The net retention volume V is equal to the retention volume minus the column dead space, V — where both V and are corrected for the pressure-gradient correction factor (see below). If the noncolumn contributions to the dead space are insignificant relative to the total dead space, and if the sample size is small enough so that the velocity of the mobile phase within the band is not increased by the solute in the mobile phase, then the net retention volume is equal to kV, and the partition ratio is (V — F )/F . The relative retention for two solutes is the ratio of their net retention volumes (V2 — or Fj/Fj this is usually expressed by a... 

Strongly dependent on temperature for both gases and liquids. For gases the effective flow rate also may change with temperature, owing to changes in the pressure-gradient correction factor. 

Figure 5. Sublayer burst period data in Newtonian and drag-reducing flows. The solid line represents both visual and hot-wire data in a water channel flow. Open and closed circles in the upper part of the plot represent two-dimensional visual water and polymer data, with the dashed line a pressure gradient correction. All other symbols are autocorrelation data, open for solvent, closed for polymer solutions (including open and closed circles in the lower part of the plot). Ekses are water, circled ekses are polymer circled dots are water, half-black squares and circles are polymer.

Pressure Gradient Correction Coefficient j. This factor corrects for the compressibility of the mobile phase in a homogeneously filled column of uniform diameter ... 

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