Origin

The first fundamental work was published by Small in 1974. The term hydrodynamic refers to the main driving force for separation. Under certain conditions, the nonturbulent flow in the column can be considered to be Poiseuille flow. Laminar flow occur-ing at a Reynolds number less than 2000 (Re = 2Rip/p, where R = tube radius, i = velocity, p = viscosity and p = density of medium), leads to a parabolic velocity profile in which the highest velocity is the centre of the tube (Figure 2A). For geometric reasons larger particles are statistically located preferentially in the axis of the capillary, whereas smaller ones are close to the walls. This difference in flow velocity is one of the separation mechanisms. Electrostatic effects must also be taken into account (Figure 2B).

The term separation by flow was initially proposed. Liquid exclusion chromatography has been used with porous packing. HDPC refers to a combined permeation and hydrodynamic process on small pore particles and porous hydrodynamic chromatography is used in packing with large pores. For capillary chromatography in more restricted conditions, another term has been used: tubular pinch chromatog-

Figure 1 Calibration curves: (A) RF versus sample diameter (Dp) at flow rates 0.5-2.5 mL min and (B) log sample diameter versus elution volume (V). (Reproduced with permission from Revillon A and Boucher P (1989) Capillary hydrodynamic chromatography: Optimization study. Journal ofApplied Polymer Science: Applied Polymer Symposium 43: 115.

Figure 1 Calibration curves: (A) RF versus sample diameter (Dp) at flow rates 0.5-2.5 mL min and (B) log sample diameter versus elution volume (V). (Reproduced with permission from Revillon A and Boucher P (1989) Capillary hydrodynamic chromatography: Optimization study. Journal ofApplied Polymer Science: Applied Polymer Symposium 43: 115.

Figure 2 (A) Radial velocity in laminar Poiseuille flow (SFFF, steric FFF) and (B) concentration profile of particles under the effect of double-layer (DC) and van der Waals (VDW) forces (r, variable along radius of column; z, direction of flow). (Reproduced with permission from Revillon A (1996) Chromatographie hydrodynamique a colonne capillaire et a colonne remplie. In: Cavaille JY, Garcia-Ramirez M and Vigier G (eds) Polymères: de la polymérisation auxpropriétés, pp. 167-174. Paris: Polytechnica.)

Figure 2 (A) Radial velocity in laminar Poiseuille flow (SFFF, steric FFF) and (B) concentration profile of particles under the effect of double-layer (DC) and van der Waals (VDW) forces (r, variable along radius of column; z, direction of flow). (Reproduced with permission from Revillon A (1996) Chromatographie hydrodynamique a colonne capillaire et a colonne remplie. In: Cavaille JY, Garcia-Ramirez M and Vigier G (eds) Polymères: de la polymérisation auxpropriétés, pp. 167-174. Paris: Polytechnica.)

raphy. In slalom chromatography, the hydrodynamic effect in the interstices between particles leads to increasing elution volume with sample size.

A more frequently used alternative is hydrodynamic fractionation, since the process involved is not a classical chromatographic one of mass distribution equilibrium between two phases. In fact, there is only one phase, the mobile phase as an eluent, and only one field, the hydrodynamic one (Figure 2A). In FFF, a set of techniques for particle sizing, another external field is added. The intention is to modulate the intensity of the second field to inverse the elution order (e.g. in steric FFF). In HDC with packed columns, the nonporous stationary phase is theoretically inert. For porous packings, which allow the use of smaller capillaries, the SEC process operates simultaneously with HDC. Improvements on the original process are described in many papers and have been developed mainly at Lehigh University by Silebi and co-workers.

Solar Panel Basics

Solar Panel Basics

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