Plate Theory and Extensions - Experimental Examination of Dead Volume Measurement > Page 40

Pore Volume Containing Components of the Mobile Phase Having

Composition Differing frof the Moving Phase, by difference   0.18 ml 

Pore Volume Containing Mobile Phase of the Same

     Composition as the Moving Phase, by difference               0.70 ml

A summary of the data for the Zorbax column obtained by Alhedai et al. [11] is shown in Table 2. The distribution of the various chromatographically important volumes within a column is neither simple nor obvious. From the data it appears that 70% of the column volume is occupied by mobile phase but only about 50% of that mobile phase is actually moving. In addition, about 18% of the mobile phase is interstitial, but static, and about 31% of the mobile phase is contained within the pores and is also static. Just over 6% of the mobile phase in the pores has a different composition to that of the mobile phase proper and, thus, constitutes a second stationary phase.

Good agreement was obtained between the different methods of measuring the thermodynamic dead volume. Weighing the column filled with mobile phase and then weighing dry, measuring the retention volume of one pure component of the mobile phase and measuring the retention volume of a completely permeating solute by extrapolation, all give very closely similar values.

 About 12% of the column volume is occupied by the stationary phase, which is equivalent to about 17% of the mobile phase content of the column.  The values given in Table 2 are probably representative of most reverse phase columns but will differ significantly with extremes of pore size and pore volume.