Plate Theory and Extensions - The Compressibility of the Mobile Phase > Page 24
Equation (23) allows the ratio to be calculated along the length of the column for different inlet/outlet pressure ratios. Using equation
(23), the values of at different points along the column were
calculated and the results shown as curves relating to fraction of the column length are shown in Figure 4.
Figure 4. Graph Showing Change of Pressure Along a GC Column for Different Inlet/Outlet Pressure Ratios
At low inlet/outlet pressure ratios (i.e., g < 2), the pressure falls almost linearly from the inlet to the outlet of the column. At high inlet/outlet pressure ratios, (i.e., g > 2), the relationship is no longer linear and the pressure falls very rapidly in the latter half of the column. It is obvious that the average flow rate can not be used for measuring retention volumes and a correction factor must be employed.