Filter media, commercially available

Three filtering media commercially available from Millipore Corporation were evaluated for the collection of airborne particulates of the organoarsenical compounds. These were (l) cellulose ester membranes (2) Fluoropore and (3) Mitex. The cellulose ester membrane filters (0.8 ym pore size) are the standard Millipore filters used for aerosol sampling and consist of a mixture of cellulose nitrate and cellulose acetate. The Fluoropore filters are made of Teflon (PTFE) and are bonded to a polyethylene net. Fluoropore filters with a pore size of 1.0 ym were selected for this study. 

This technology has been demonstrated in bench-, pUot-, and full-scale applications. The Bohn Biofilter Bohn off-gas treatment (TO 130) is one example of a commercially available biofilter system that uses compost or soil as the filter medium. 

Three commercially available filtering media were evaluated for the collection of airborne particulates of the organoarsenical compounds. These were cellulose ester, Fluoropore, and Mitex membrane filters. The evaluation was based on the following requirements l) the collection medium must quantitatively collect the particulates 2) the collection medium must be capable of. retaining the compounds without loss or chemical change before analysis 3) the collected species must be extracted quantitatively from the collection medium for analysis and b) the method must be efficient at temperatures up to 50°C and a relative humidity of... 

The most important technique for perfusion culture methods is to separate the concentrated cells and conditioned medium from the suspended culture broth. As noted above, the separation methods chiefly used are filtration with tubular and flat membranes as well as ceramic macroporous filters. These membrane reactors can be employed for both anchorage-dependent and suspension growing cells. Static maintenance type systems are commercially available for disposable reactors, and small size unit reactors from 80 ml to 1 liter are used for continuous production of monoclonal antibodies with hybridoma cells. The maintainable cell densities are about 10 -10 cells/ ml which is essentially mouse ascites level. However, in these systems, the cell numbers cannot be counted directly because the cells adhere to membranes or hollow fibers. Therefore, the measurement of cell density must use indirect methods. Such indirect methods include the assaying of the quantities of glucose consumption and the accumulation of lactate. The parameters of scale-up have not yet been established for these static methods. 

The dip slide process is based on the membrane filter method. It uses commercially available test kits, comprising a nutrient medium carrier in which the medium part is inserted in a beaker. This beaker serves as dipper for taking the water sample and also protects the nutrient medium part from secondary infection and from drying out during the incubation period. 

In some cases of pilot scale filtration, entire units have been enclosed as a secondary containment precaution (see Chapter 8). A recent commercial development is the MBR-Sultzer dynamic filter which is available in three sizes. Dynamic filtration is the same as cross flow filtration with little or no recirculation. The cross flow effect is derived from the spinning of the inner surface filter. This type of filter is more efficient, has a lower pump rate and a much higher linear velocity across the filter surface, than conventional cross flow filtration units. There is also little or no damaging effect on sensitive cells. The medium size has the same capacity as the Westfalia SA-7 separator. Van Hemert and Tiesjema concluded that the dynamic filter is suitable for work requiring strict aseptic and primary containment conditions. The use of a double mechanical seal on the rotating shaft could offer a higher degree of containment if required. 

Cellulose acetate as a medium for electrophoresis was introduced by Kohn in 1958. It was developed from bacteriological cellulose acetate membrane filters and is commercially available as high purity cellulose acetate strips, which are thin and have a uniform micropore structure. 

Photochemical syntheses, as well as photodegradation studies, are usually performed in irradiation reactors a variety of different designs are commercially available, depending on the specific application requirements. For synthetic photochemistry, immersion well reactors are commonly used (Fig. 14.4). The source, typically a low or medium pressure mercury lamp, is housed in a double-walled quartz jacket, which allows water-cooUng and/or filtering of excitation radiation. The solution to be irradiated surrounds the lamp source, enabling homogenous irradiation. 

Many different types of filters are available commercially. They can be broadly classified into two types with, however, some overlap. Fibrous filters are composed of mats of fi bets that may be ntade of cellulose, quartz, glass, polymeric materials, or metals. Porous membrane filters are usually composed of thin films of polymeric materials 0.05 to 0.2 mm thick sufficiently porous for air to How through under pressure. Pore size is controlled in the manufacturing process and ranges from 0.02 to 10 /rm, A significant fraction of the panicles may be caught on the upstream surface of the filter, but some particles may also penetrate and be caught inside the pores of the medium as well. 

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