Gradient elution mode retention factor

Once the retention volume of a solute is calculated for a particular gradient profile, corresponding bandwidth and resolution can be determined by introducing the appropriate instantaneous retention factor A, at the elution of the peak maximum calculated from the gradient function tpf = /(Tr) and from the retention equation A, = f chromatographic mode and gradient function used [851 ... 

In HIC, molecules are bound with a high concentration of salt, usually ammonium or sodium sulfate (1-2 A/) in a buffer (0.02-0.05 M). Elution is attained by a gradient to a lower concentration of salt in the buffer. The pH is controlled and is usually in the range of 6-8, but it is not a critical factor in selectivity. Additives to enhance protein stability are generally compatible with the process. Contrary to its effect on other modes of chromatography, reducing the temperature decreases the retention in HIC due to its being an entropy-driven technique. 

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