Separation Mechanisms

Two particular mechanisms, polarization and focusing, can govern the separation. The components of the fractionated sample can be differently compressed to the accumulation wall of the channel or focused at different levels. Polarization and focusing FFF have many common characteristics such as the experimental procedures, instrumentation, data treatment, and the range of potential applications. The separation is carried out in one liquid phase. The absence of a stationary phase of large surface area can be of fundamental importance for the fractionation of biological particles whose stability against degradation can be sensitive to interactions with the surfaces. The strength of the field can be easily controlled to manipulate the retention. Many operational variables can be programmed.

The polarization FFF methods are classified with regard to the character of the applied field, while the

Figure 2 Schematic representation of the general principle and experimental arrangement of field-flow fractionation: (1) pump; (2) injector; (3) separation channel; (4) external field; (5) hydrodynamic flow; (6) detector.

focusing FFF methods are classified according to the combination of various fields and gradients. Although some earlier separation methods are also based on the coupled action of field forces and hy-drodynamic flow, the beginning of FFF proper can be attributed to Giddings who in 1966 described the general concept of polarization FFF. Focusing FFF was originally described in 1982.

Polarization FFF methods make use of the formation of an exponential concentration distribution of each sample component across the channel with the maximum concentration at the accumulation wall which is a consequence of constant and position-independent velocity of transversal migration of the affected species due to the field forces. This concentration distribution is combined with the velocity profile formed in the flowing liquid.

Focusing FFF methods make use of transversal migration of each sample component under the effect of driving forces that vary across the channel. The particles are focused at the levels where the intensity of the effective forces is zero and are transported longitudinally according to their positions within the established flow velocity profile. The concentration distribution within a zone of a focused sample component can be described by a nearly Gaussian distribution function.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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