Band broadening compressible mobile phases

For an understanding of band broadening in chromatographic systems, the linear velocity of the mobile phase is more important than the column volumetric flow rate. Complications in identifying a suitable velocity arise for compressible mobile phases... 

A. D. Jerkovich, J. S. Mellors, J. W. Thompson, and J. W. Jorgenson, Linear velocity surge caused by mobile-phase compression as a source of band broadening in iso-cratic ultrahigh-pressure liquid chromatography, AnaZ. Chem. 77 (2005), 6292-6299. 

Most enantiomer separations depend, at least in part, on multiple polar interactions between the enantiomers and chiral selector to form diastereomer complexes. These complexes are often too stable for the enantiomers to be eluted by carbon dioxide in the absence of polar modifiers. Optimum resolution is usually observed at low temperatures, frequently subcritical. These conditions typically result in increased peak separations accompanied by increased band broadening. The observed change in resolution depends on which factor is dominant. Mobile phase composition and temperature are the two most important parameters for optimizing resolution in the minimum separation time pressure is often less important as the modified mobile phases are not very compressible. 

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