Ultrahigh-pressure liquid chromatography: fundamental aspects of compression and decompression heating

Ultrahigh-pressure liquid chromatography is an emerging technique for carrying out rapid and highly efficient separations. Unfortunately, one of the simplifying assumptions made in conventional high-performance liquid chromatography, incompressibility of the mobile phase, is not valid when higher and higher pressures are used. Rather, both compression and decompression of the eluent must be considered in terms of both heating and changes in the solvent's structure. The first of these problems, eluent heating during the compression and decompression cycles, which occurs in the pump and column, respectively, are considered in terms of a combined first principle-empirical approach that is solved (i.e., an analytic solution obtained from the resulting integral equation) using 0.01 Bar pressure steps. The approach is used to estimate compression and decompression heating for methanol and water.