Chromatography effective capacity ratio

The pH effect on the molecular interactions can be examined experimentally using liquid chromatography. The capacity ratio in an eluent of a given pH can be predicted from and the MI energy at a given pH can be calculated using eqn (4). 

The capacity ratio of a solute (k ) was introduced early in the development of chromatography and was used as an alternative means of identifying a solute as the measurement eliminated the effect of flow rate. The capacity ratio was defined as the ratio of the distribution coefficient of the solute to the phase ratio (a) of the column. In turn, the phase ratio of the column was defined as the ratio of the volume of mobile phase in the column to the volume of stationary phase in the column. 

The capacity ratio of partially ionized compounds can be predicted using eqn (9). For evaluation by the above approach, and ki were replaced with molecular interaction energy values. The p Ta values predicted from the atomic partial charge, related to the measured pXa values in liquid chromatography, were used for the calculation, and the concentration effect of an organic modifier (0.022 pH units per % methanol from ref. 36) was added for the calculation. The predicted p Ta values derived from Hammett s equation were used for further evaluation. The results are shown in Figure 6.26. 

Kautz, C.B., Dahlmann, U.H., and Schneider, G.M. (1997) Capacity ratios in supercritical fluid chromatography Effect of mobile and stationary phase on hexasubstituted benzenes, J. Chromatogr. A 776, 305-309. 

The effect of temperature on column efficiency, however, is frequently exploited, particularly in size exclusion chromatography (SEC). As has already been discussed, high efficiencies are essential in SEC due to the limited peak capacity of the column and consequently, the very small separation ratios. However the effect of temperature on column efficiency is not well understood by many analysts and consequently, will be discussed in some detail. It was shown on page... 

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