In addition it would be impossible to place a small enough charge on the column, even with the most sophisticated capillary column sampling techniques. As the temperature rises, the (k') value and the retention ratio decreases resulting in an increase in column length and an increase in analysis time. When the temperature has reached 120 C the column length is 1 m, and with great experimental care, this column could probably be satisfactorily used with the most sensitive detectors and with a split injection procedure. As the temperature rises still further the temperature of co-elution is approached (where the elution order is reversed) and the retention ratio becomes very small and exceedingly long columns (1000 m) would be necessary to effect a separation. This would be accompanied with proportionally long analysis times. In fact, at the temperature of co-elution, the column length and the analysis time would be infinitely large. It is interesting to see that the effect of further increase in temperature results in an increase in the retention ratio (a ratio of 0.91 is equivalent to 1.1 after the elution order is reversed) and thus the minimum column length is reduced. However, the (k') values also falls as the retention ratio increases and eventually the effect of the very small (k') value will dominate the demand for theoretical plates. Thus, although the retention ratio continues to increase, the minimum column length also increases accompanied by a proportional increase in analysis time. It is seen that although the various effects can be explained on a theoretical basis, the relationship between optimum column length and analysis time with temperature is complex and each separation will need to be assessed on its own characteristics.

It should be emphasized that although the curves shown in figure 52 are generally of a form that will be exhibited by all enantiomeric pairs, they are specific to the enantiomers of phenylethanol. They are, therefore, unique to that substance and the numerical values shown will digress considerably between different enantiomeric pairs.