Porous hydrodynamic chromatography

Kraak, J., Ostervink, R., Poppe, H., Esser, U., Unger, K. K. Hydrodynamic chromatography of macromolecules on 2 im non-porous... 

One of these proposed a non-equilibrium process in which the separation was controlled by differing rates of diffusion for different molecular masses [23]. Other workers have proposed a separation by flow mechanism [24, 25] in which the larger molecules are excluded from the surface of the gel particles and remain in the centre of the solvent channels and are thus eluted first. The original theory did not invoke a porous structure for the gel, but this was modified later. The mechanism bears resemblance to that proposed for hydrodynamic chromatography (see Chapter 10). A further model suggested that the pore size distribution of the gel was directly responsible for its ability to separate molecules by size, and that there is a one-to-one correspondence with size of pores and size of molecules [26]. All these theories have been critically reviewed in the book by Yau et al [6]. 

This chapter deals with the application of size exclusion chromatography to the analysis of particle size (PS) and particle size distribution (PSD) of submicron colloidal systems. The technique which will be discussed is known as hydrodynamic chromatography, or HDC. It is a variation on the SEC method in which the separation columns are packed with non-porous rather than porous beads. In addition, in HDC, the solute to be fractionated is particulate rather than molecular. The overlap between SEC and HDC systems is evidenced by the comparisons listed in Table 10.1. 

G. Stegeman, R. Oostervink, J.C. Kraak, H. Poppe, and K.K. Unger Hydrodynamic chromatography of macromolecules on small spherical non-porous silica particles, J. Chromatogr. A, 506 (1990) 547-561... 

Stegeman, G., Kraak, J. C., and Poppe, H., Hydrodynamic and size-exclusion chromatography of polymers on porous particles, ]. Chromatogr., 550, 721, 1991. 

GPC is a further special form of liquid chromatography. The separation column is packed with porous, polymer gels (e.g. polystyrene gel) as stationary phase. The particle size of the packing material and the size distribution of the pores are well defined and uniform. In GPC molecules are separated according to their effective size in solution, i.e., their hydrodynamic volume, and not according to their affinity for the support material. 

Such precise control of porous properties is expected to be very useful in the design of specialized CEC columns for separation in modes other than reversed-phase. For example, size exclusion chromatography (SEC) is an isocratic separation method that relies on differences in the hydrodynamic volumes of the analytes. Because all solute-stationary phase interactions must be avoided in SEC, solvents such as pure tetrahydrofuran are often used as the mobile phase for the analysis of synthetic polymers, since they dissolve a wide range of structures and minimize interactions with the chromatographic medium. Despite the reported use of entirely non-aqueous eluents in both electrophoresis and CEC [65], no appreciable flow through the methacrylate-based monoliths was observed using pure tetrahydrofuran as the mobile phase. However, a mixture of 2% water and tetrahydrofuran was found to substan-... 

In Fl-FFF, the channel is created by placing a mylar spacer with the channel cut out between two porous frits. A membrane hlter of a specihc molecular weight cutoff is placed on one of the frits and acts as the accumulation wall to permit flow, without loss of particles. The applied force is then a perpendicular flow of the carrier solution across the porous frits. Fl-FFF is a versatile technique capable of separating macromolecules as small as roughly 1000 Da, in which case it is comparable to gel permeation (size exclusion) chromatography. However, Fl-FFF can also be applied to the separation of colloidal particles. In this case the hydrodynamic diameter of the colloidal particle is related to the retention volume, V by the equation... 

HP-SEC, also called high-performance gel-permeation chromatography (HP-GPC), is performed on porous stationary phases and separates analytes according to their molecular mass or their hydrodynamic volume. As a nonretentive separation mode, HP-SEC is usually operated with isocratic elution using aqueous low salt mobile... 

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