Field flow fractionation sedimentation 278, centrifugal

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

Fig. 10. Centrifugal sedimentation field-flow fractionation equipment deposits particles along the circumference of the disk by size. The fluid enters and...

Fig. 5.11 Centrifugal sedimentation field flow fractionation. 5.21.3 Time-delayed exponential SFFF...

Koehler and Provder [317] sized monodisperse PMMA latexes with a range of instruments Disc centrifugal sedimentation (DCP), sedimentation field flow fractionation (SFFF), hydrodynamic chromatography (HDC), photon correlation spectroscopy (PCS), turbidimetry and transmission electron microscopy (TEM). TEM gave the smallest sizes, DCP and SFFF were in fair agreement in the center and PCS the highest sizes. 

Field-flow fractionation (FFF) technology is applicable to the characterization and separation of particulate species and macromolecules. Separations in FFF take place in an open flow channel over which a field is applied perpendicular to the flow. Among the various FFF subtechniques, depending on the kind of the applied external fields, sedimentation FFF (SdFFF) is the most versatile and accurate, as it is based on simple physical phenomena that can be accurately described mathematically. SdFFF, which uses a centrifugal grav-... 

Sedimentation Field Flow Fractionator. The chromatography-related principle of this particle size and size distribution analyzer is based upon the interaction of the particle suspension under centrifugal field motion in a thin channel. The elution time of the particles is a function of particle size, particle density, flow rate of mobile phase, density of mobile phase, and the centrifugal force applied. After the size separation has occurred, the particles are detected in the mobile phase using a turbidity detection system. The dynamic range of the instrument is dependent on particle density and operating conditions and is typically within 0.03 /rm— 1 /rm range. 

This section addresses two basic principles of classification—sedimentation and field-flow fractionation—and the corresponding sizing techniques. Additionally, a chromatographic technique is briefly introduced. The focus lies on sedimentation or centrifugation analysis, which corresponds to its practical relevance for the characterisation of coUoidal suspensions. 

Field flow fractionation (FFF) can also be used for microbial cell separation. In the FFF technique, a field (may be gravitational, centrifugal, thermal-gradient, electrical, magnetic, etc.) is applied perpendicular to the fluid flow, causing particles to migrate with different velocities. Fields of sedimentation, diffusion, and electrical diffusion are manipulated to optimize the separations of microbes. Separation of Pseudomonas putida and E. coli has been achieved by hyperlayer FFF. Fractions of the whole cells were collected after the separation at different time intervals, dif-... 

Sedimentation Field-Flow Fractionation This method uses the centrifugal field to separate molecules. The value of A, is calculated by using... 

Thickeners are used to concentrate dilute suspensions in preparation for further separation in filters and centrifuges. As previously shown in Table 3, thickeners frequently lead to removal of a large fraction of the liquid in a slurry. A schematic continuous thickener is shown in Fig. 24. In the figure, a clear liquid overflows the top while a thickened sediment flows out of the bottom as underflow. Thickeners are widely used in fields sueh as wastewater, aluminum, coal, pulp and paper, cement, and sugar. 

The classification into different size fractions can be realised by gravitation (sedimentation FFF), by centrifugal fields (centrifugation FFF), by thermophoresis in temperature gradients (thermal FFF), by electric fields (electrical FFF), or by hydrodynamic fields, i.e. crossflow through the wall(s) (flow FFF). Even though the main fields of application are coUoidal systems, one can also employ FFF for the classification of micrometre particles (x > 1 pm). In that case, diffusion can be usually neglected, yet hydrodynamic lift forces and steric effects counteract the external field and cause a reversal of the size dependency. 

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