Filtration Spin-filters

When bioreactors coupled to cell retention devices are used, it is also necessary to evaluate the scale-up of the cell separation equipment. In the case of the spin-filter (see Chapter 11), parameters such as filter rotation velocity and the ratio of filtration area to bioreactor working volume are particularly relevant (Deo et at, 1996). 

Filtration is a unit operation commonly employed nowadays in biotechnological processes. In this unit operation, a filter medium acts as a physical barrier to particles larger than its pores. Traditional filtration devices such as filter presses and rotary vacuum drum filters have so far found no application for the separation of animal cells. Nevertheless, membrane filters are commonly employed, as well as some alternative filter designs such as spin-filters. In the next sections, the most common types of filters used for animal cell separation will be discussed. 

Favre (1993) found that his data for constant volume perfusion of two different mouse-mouse hybridoma lines could not fit the classical constant volume filtration equation. He suggested that this could be due to a monolayer type of cell buildup instead of a cake in the conventional filtration. According to Favre, a model principally based on stochastic and steady plugging of the pores in the screen by the cells leading to an equilibrium state can possibly give a rational design procedure for spin filters. 

Height of spin filter over which filtration occurs (m)... 

Electrocompetent cells were transformed using MicroPulser electroporation cuvettes (Bio-Rad). Purification of His-Tag fusion proteins was conducted using a Hi-Trap Chelating column (GE Healthcare), and any subsequent gel filtration steps were carried out on Superdex 75/200 columns (GE Healthcare) depending upon protein size. Proteins were concentrated using Vivaspin 20 ultrafiltration spin filters (Sartorius) with a 5 kDa or 30 kDa cut-off depending upon the size of the protein. 

The polymer can easily be recovered by simple vacuum filtration or centrifugation of the polymer slurry. This can be followed by direct conversion of the filter cake to dope by slurrying the filter cake in chilled solvent and then passing the slurry through a heat exchanger to form the spinning solution and a thin-film evaporator to remove residual monomer. 

In the filtration of small amounts of fine particles from liquid by means of bulky filter media (such as absorbent cotton or felt) it has been found that the preceding equations based upon the resistance of a cake of solids do not hold, since no cake is formed. For these cases, in which filtration takes place on the surface or within the interstices of a medium, analogous equations have been developed [Hermans and Bredee, J. Soc. Chem. Ind., 55T, 1 (1936)]. These are usefully summarized, for both constant-pressure and constant-rate conditions, by Grace [Am. In.st. Chem. Eng. J., 2, 323 (1956)]. These equations often apply to the clarification of such materials as sugar solutions, viscose and other spinning solutions, and film-casting dopes. 

Pressed Felts and Cotton Batting These materials are used to filter gelatinous particles from paints, spinning solutions, and other viscous liquids. Filtration occurs by deposition of the particles in and on the fibers throughout the mat. 

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

In a ID COSY-RELAY experiment [38] (fig. 13(a)) a multistep relay transfer is applied after the filtration. If the filtration is performed on the H-2 proton, the CSSF is incorporated into the first spin-echo. If there is not sufficient chemical shift separation between H-2 protons, the filter is shifted to the second spin-echo. The method is illustrated for the separation of the spin systems of two terminal /3-glucopyranose residues of a modified LPS (5) containing a total of nine saccharide units [76]. The anomeric proton resonances of the two /3-glycopyranoses overlapped almost completely, with a chemical shift difference of only 1.9 Hz, while the corresponding H-2 resonances were separated by 55.0 Hz. The length of the filtration interval, Ti, was adjusted to yield a maximum antiphase magnetization of H-2 pro-... 

In all CSSF experiments filtration was performed immediately after the COSY step. Should there not be a sufficient chemical shift separation between H-2 protons, the magnetization could be further transferred along the spin system and filtered during one of the later spin-echoes. We note that such extensive transfer of magnetization can bring some signal attenuation due to the relaxation losses and a compromise setting of spin-echo intervals. 

Separate yolks of chicken eggs from egg white and discard egg white. Wash the yolks carefully with water to remove adhering egg white. Suspend the yolks in 5 vol. Soln. A by vigorous stirring. Precipitate lipids and lipoproteins by addition of 6 ml Soln. B and 15 ml Soln. C per 100 ml yolk suspension. Stir at RT for 30-60 min and spin at 5000 x g for 10 min. Wash the pellet with a small volume of Soln. A (about 20 ml per yolk) and centrifuge again. Combine the supernatants and filter through a paper filter. Add Soln. D to the clear filtrate to a final concentration of 30 mM EDTA. 

Reaction of Acetoin (3-Hydroxy-2-butanone) with Ammonia. Aqueous solution of ammonium hydroxyde (20%, 100 ml) was added to acetoin (17.6 g, 0.2 mol) and the reaction mixture was stirred for 30 min at 50°C and then for 6 h at room temperature. The precipitated product was filtered off, the filtrate was neutralized with 10% hydrochloric acid, and extracted with ether (continuous overnight extraction). The extract was washed with water, dried over anhydrous sodium sulfate, and concentrated on a spinning-band distillation apparatus. The residual solution was then analyzed by GC and GC-MS. 

To a stirred solution of 7-([2-(benzoyloxy)ethoxymethyl]formylaminoJ-5-(methylsulfanyl)furazano[3,4-(flpyrimidine in HOAc (200 mL) that was cooled on a water bath was added Zn powder (30 g) in portions Over 20 min. The resultant mixture was refluxed with stirring for 1.5 h. The mixture was cooled and filtered to remove the solids. The solids were washed with HOAc, and the filtrate and wash were spin evaporated in vacuo. The residue was covered with H O (100 mL) and turned on a rotary evaporator without heating until a solid formed. The aqueous layer was decanted and the solids were digested with EtOH (50 mL) and allowed to coo). The solids were collected, washed with EtjO, and dried yield 3.30 g (32%) mp 166-167 "C. 

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