Overloaded isocratic elution

In cases where mass transfer is rapid, as is the case with most small molecule separations, then isocratic elution can offer advantages such as automatic fraction reprocessing and solvent recycle. However, with larger synthetic objectives the rate of mass transfer is comparatively low so isocratic elution leads to band broadening and subsequently to recovery of the peptide at high dilution. Most preparative HPLC based peptide separations are carried out under gradient and overload conditions that allow for maximum throughput in terms of time and quantity. 

FIGURE 10.22 Optimum separations for isocratic overloaded elution for the purification of the less retained component. The production rate (left) and the product of the production rate and the recovery yield (right) were maximized, respectively, a=1.2 k=2 C = C = lOOmg/mL. (Reproduced from Felinger, A. and Guiochon, G., J. Chromatogr. A, 752, 31, 1996. With permission from Elsevier.)... 

Overloaded elution chromatography Name given to elution chromatography when a large sample is used, so the column is operated imder nonlinear isocratic conditions. This distinguishes the preparative applications of elution from its analytical applications, which use small samples. 

---