The Thermodynamics of Chromatography - Other Thermodynamic Methods that are Used for Studying Chromatographic Systems > Optimum Operating Conditions for Chiral Separations in Liquid Chromatography > The Effect of Temperature and Solvent Composition on the Required Column Efficiency > Page

   

 

The Effect of Temperature and Solvent Composition on the Required Column Efficiency

Using the values for the capacity ratios and separation ratios derived from equations (47), (48) and (49) in equation (39) the efficiency necessary to ensure a separation of (6s) for the two enantiomers can be calculated over a range of temperatures and solvent compositions.

Figure 22. Graphs of Required Efficiency against Temperature for Each Solvent Composition

Curves relating required efficiency against temperature for each solvent composition, calculated in this manner, are shown in figure 22. As would be expected, the minimum efficiency is required at the lowest temperature and lowest ethanol concentration. As either the separation ratio and/or the capacity ratios decrease, the necessary efficiency to achieve a separation increases (as predicted by equation (39)). At one extreme, where the capacity ratio is very small (i.e. at 50% v/v ethanol and 50˚C), 15000 theoretical plates is necessary for separation. However, if the volume fraction of ethanol is set at 0.05, then even at 50˚C, separation is achieved with less than 3000 theoretical plates.