Solutes, column-packing structure

The large porous particles are the oldest of these materials, and are no longer used in analytical hplc, although because of their high sample capacity they are still useful in preparative work. Columns packed with the large particles have relatively low efficiencies because of the long time it takes for solute species to diffuse into and out of the porous structure (slow mass transfer). 

Minimized interaction between eluite molecules and column packing is operative in hydrophobic interaction chromatography where biological solutes are so mildly bound to a stationary phase that their delicate native tertiary structure is not spoiled. This separation of extreme mildness is also a separation of chemically differing species, i.e., separation by composition. 

High-purity water for special applications is obtained by distillation or by ion exchange, the exchange of one type of ion in a solution by another. In ion exchange, water passes through a column packed with a material such as zeolite, an aluminosilicate with a very open structure that can capture ions such as Mg2+ and Ca2+ and exchange them for H+ ions (see Box 13.4). 

On the other hand, the lack of internal pore structure with micropellicular sorbents is of distinct advantage in the analytical HPLC of biological macromolecules because undesirable steric effects can significantly reduce the efficiency of columns packed with porous sorbents and also result in poor recovery. Furthermore, the micropellicular stationary phases which have a solid, fluid-impervious core, are generally more stable at elevated temperature than conventional porous supports. At elevated column temperature the viscosity of the mobile phase decreases with concomitant increase in solute diffusivity and improvement of sorption kinetics. From these considerations, it follows that columns packed with micropellicular stationary phases offer the possibility of significant improvements in the speed and column efficiency in the analysis of proteins, peptides and other biopolymers over those obtained with conventional porous stationary phases. In this paper, we describe selected examples for the use of micropellicular reversed phase... 

A packed coltimn is not so flexible. The usual spacing of distributors is 3-4 m (six to eight theoretical stages) and even a high efficiency packed column will seldom have more than three or four intermediate distributors in the column and these are the only positions into which the feed can be inserted or a liquid side stream removed. A feed with salts or polymers in solution may block packing, structured or random, near the feed point. This is much less likely with trays. 

This universal calibration procedure is widely used for many different polymer types [9,10] the procedure can be used to allow for differences in morphology as well as differences of chemical type. However, it is important to note that the procedure cannot be applied to all polymer types exceptions are often found when the polymer molecule has some structure when in solution, or when there are unwanted interactions between the solute and the column packing. 

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