Combined use of temperature and solvent strength in reversed-phase gradient elution .2. Comparing selectivity for different samples and systems

A change in temperature (T) or gradient steepness (b) can result in changes in reversed-phase selectivity (alpha). The magnitude of these changes in alpha will vary with ether separation conditions (column, pH, etc.) and with sample type. In this paper, selectivity changes as a function of T and b are discussed and a simple treatment that allows changes in selectivity to be compared quantitatively for different samples and HPLC conditions is developed. Following papers in this series will apply this theory to arrive at conclusions concerning the use of temperature and gradient steepness in HPLC method development. The present treatment assumes that gradient-steepness selectivity (measured by the parameter S) does not change significantly with temperature. Data for a wide range of compound types and conditions are provided in support of this assumption.