CHAPTER 21 - ADSORPTION PROBLEMS IN PREPARATIVE AND ANALYTICAL LIQUID CHROMATOGRAPHY

Abstract

This chapter analyzes adsorption problems in preparative and analytical liquid chromatography (LC). The goal of adsorption in LC, as with other closely related techniques like TLC, is always separation. Often a selective separation is also required. In analytical LC, the function of separation is quantitation whether approximate or very precise. In preparative LC, separation is made with recovery in mind. Compared to gas chromatography (GC), the mechanism of actual separation is much more complex, much less well understood and capable of far more variation. The latter facet makes the technique both more difficult and more powerful than GC. In many, if not most separations, more than one mechanism is operating. In exclusion chromatography, separation depends on some molecules being about the same size as the pores in the packing material. Molecules that are too big are excluded completely and only travel in the interparticle spaces. Those molecules that are much smaller than the pores diffuse in and out of the pores and are eluted in one column volume, while those molecules that are nearer to the pore size tend to spend less time in the pores and elute in smaller volumes.