Centrifugal filtration technique

The separation of cells from the culture media or fermentation broth is the first step in a bioproduct recovery sequence. Whereas centrifugation is common for recombinant bacterial cells (see Centrifugal separation), the final removal of CHO cells utilizes sterile-filtration techniques. Safety concerns with respect to contamination of the product with CHO cells were addressed by confirming the absence of cells in the product, and their relative noninfectivity with respect to immune competent rodents injected with a large number of CHO cells. 

To realise this, first very homogeneous OC-AI2O3 supports were prepared by using colloidal techniques. Colloidal filtration was used for the preparation of flat supports, while a centrifugal casting technique was developed to prepare highly smooth and round tubular supports. 

Clean-up procedures involve the separation of analyte(s) from other sample components that might otherwise make the analysis more difficult. Filtration, sublimation and centrifugation are techniques that can be used for sample clean-up. 

The checker reports that standard filtration techniques can be substituted for the centrifugation steps. The reaction of hydrous niobium (V) oxide is done in a 100-ml. round-bottomed flask fitted with an outer standard-taper joint. The solution of niobium(V) chloride in thionyl chloride is filtered by attaching a filter tube (having a standard-taper inner joint at each end) with a medium-porosity sin-tered-glass filter to the neck of the reaction flask, attaching another 100-ml. round-bottomed flask to the opposite end of the filter tube, and inverting the assembly. The residue can be washed with small aliquots of thionyl chloride. With this kind of apparatus the synthesis can be scaled up by a factor of 10 or more. 

The yeast produced by continuous culture techniques is separated from the liquid medium and solvent washed by centrifugation or filtration techniques. After drying, a protein supplement is obtained, which contains 65-68% protein and is suitable for addition to animal feeds. This protein content compares very favorably with that of dry fish meal, which contains about 65%, and dry skim milk powder with about 32%. The SCP processes have operated on the thousands of tonne/year scale in the U.K., France, and Italy, but regulatory problems with facilities operating on unpurified gas oil feedstocks have caused some shutdowns [64]. Nevertheless, because of a cell mass doubling time of 2.5-3 hr and the efficient carbon conversion to protein of this technology, these developments deserve to be explored further. 

Particulate solid phases with a high surface/volume ratio (consequently higher efficiency) give faster reactions since the solid phase is dispersed throughout the reaction mixture, but may suffer from the necessity of more involved separation techniques such as centrifugation, filtration or special procedures (Hunter, 1980). This also makes automation more difficult. 

Another requirement is that the particle size should be minimum, for it is known that the catalytic activity of TS-1 is drastically reduced above a particle size of 0.2 micron. Preparing catalyst particles of this size requires special filtration techniques. It was found that the usual methods of filtration had to be replaced by centrifugation to obtain satisfactory results. Hence centrifugation must be used at the manufacturing level. 

In the latter case, separation can be achieved by different means (centrifugation, filtration, size exclusion chromatography, etc...) and it is assumed that the equilibrium state is not modified during the separation step. This condition is not necessarily fullfilled, especially when the dissociation constant is sufficiently high. Separation techniques must then be extremely rapid in the case of loosely bound complexes. 

Centrifugal filtration is a complex process that is dependent on a number of parameters including liquid viscosity, cake thickness, centrifugal force, screen area, and importantly, the size and packing characteristics of the particles themselves. This technique is generally not amenable to broad generalizations and is, therefore, best approached on a case by case basis. 

The standard method for determining contamination of milk by soil particles and similar dirt is in two forms. The reference method involves centrifuging after standing for 72 h and so is not used routinely. The rapid method uses a filtration technique that takes 3 min. The amount of visible dirt on the filter is compared visually with standard photographic disks and gives values in milligrams per liter. 

Sim et al. used centrifugation, dissolved air flotation and drum filtration techniques for harvesting sewage-grown algae.Centrifugation was found to be effective... 

Centrifugation Although not strictly a filtration technique, centrifugation may be used to remove suspended impurities from a liquid (1-25 mL). 8.8... 

Sometimes, centrifugation is more effective in removing solid impurities than conventional filtration techniques. Centrifugation is particularly effective in removing suspended particles, which are so small that the particles would pass through most filtering devices. Centrifugation may also be useful when the mixture must be kept hot to prevent premature crystallization while the solid impurities are removed. 

Finally, the choice of using either filtration or centrifugation for sample preparation will depend on the outcome of recovery experiments. If comparative data from the recovery experiments show higher relative recoveries using either filtration or centrifugation, the technique that yields the highest recovery becomes the method of choice for sample preparation (see Table 12). 

The fractions indicated by the bar in Fig. IB were concentrated by a 1 h centrifugation at 100 000 X g. Calcium gcumulation was assayed with CaCl using a filtration technique (Lockau, Pfeffer 1983). At 0 min, uptake was initiated by addition of ATP to 3 mM. The reaction mixture contained 5 mM MgCl The values are corrected for calcium bound in the absence of ATP (about 1.5 nmol/ mg protein)... 

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