Filtration methods, micro

In general, fungal mycelia are filtered relatively easily, because mycelia filter cake has sufficiently large porosity. Yeast and bacteiia are much more difficult to handle because of thefr small size. Alternative filtration methods, which eliminate the filter cake, are becoming more acceptable for bacterial and yeast separation. Micro-filtration is achieved by developing large cross-flow fluid velocities across the filter surface while the velocity vector normal to the surface is relatively small. Build up of filter cake and problems of high cake resistance are therefore prevented. Micro-filtration is not discussed in this section. 

Table 3 lists the sterilization methods used for sterile products. There are five basic methods—heat, gas, radiation, light, and filtration. The first four methods destroy microbial life, while filtration removes micro-organisms. Vali-... 

Due to the potential additional risks of the filtration method as compared with other sterilisation processes, a second filtration via a further sterilised micro-organism-retaining filter, immediately prior to filling, may be advisable. The final sterile filtration should be carried out as close as possible to the filling point... 

Polyesters, such as PET are now widely used in the manufacture of fibers for textiles and other applications. While PET has many desirable properties that make it suitable for manufacturing fibers, there is a continuing need for polyester fibers that have improved properties, or properties that are different from PET, thereby opening new uses for polyester fibers. For example, PEN has found applications in high performance sailcloth materials or in industrial filtration applications. Micro fibers can be obtained from fibers using a laser thinning method. ... 

Filtration methods of capturing airborne micro-organisms by drawing metered quantities of air through filters are probably the simplest methods... 

Micro filtration (MF) and ultrafiltration (MF) are typical low-driven pressure membrane processes widely applied in various chemical and biochemical processes thanks to their advantages over traditional filtration methods. They are generally a thermal and simple in concept and operation and do not involve phase changes or chemical additives. Additionally, they are modular, easy to scale-up and characterized by low energy consumptions (Mulder, 1998). 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

The major dasses of antibiotics are secondary metabolic products of micro-organisms. Many were discovered by empirically screening culture filtrates or cell extracts for antimicrobial activity. A range of techniques (examples are methods using, impregnated discs, porous cylinders, cut wells, see Figure 6.2) have been used to carry out such screening. 

In view of the above discussion, it should be clear why the author recommends that the laboratory of Neonatology precipitate proteins with a Somogyi filtrate and then perform the hexokinase procedure on the filtrate. Neither the glucose oxidase i rocedure nor the toluidine method have adequate sensitivity thout the use of special micro-equipment and speciaT techniques. 

To determine the protein concentration, use filtrates from Sephadex G-25 (Micro-Spin) columns and proceed according to the protein assay method (BioRad). The results are given in mg protein/ml. 

Protein solubilities of soy flour and extrudates in the following solvent systems were determined by the micro-Kjeldahl method ( 9). A portion (0.1 g) of finely-ground sample (No. 60 sieve) was extracted with 9.9 ml of solvent for 1 hr at room temperature followed by centrifugation and filtration. An aliquot of the supernatant was used for nitrogen determination. 

Kawahara [156] introduced pentafluorobenzyl esters, prepared by the following procedure. A mixture of four acids (0.8 mg of each) was dissolved in 100 ml of acetone, and 250 mg (25-fold excess) of a-bromo-2,3,4,5,6-pentafluorotoluene and 50 mg (10-fold excess of potassium carbonate were added (it can be replaced with an ethanolic solution of potassium hydroxide). After refluxing for 3 h, the mixture was diluted with 500 ml of diethyl ether and 20 ml of ethyl acetate, washed with 10 ml of water and dried with 8 g of anhydrous sodium sulphate. After filtration, the sulphate and the filter were washed with 50 ml of diethyl ether, the solvent was removed and the residue was dried at 40°C and 50 mmHg it was further dissolved in 100 ml of -hexane and, after an additional 100-fold dilution, 6 /il were injected. The ECD response to pentafluorobenzoate was almost the same as that to aldrin. A method for the preparation of p-substituted benzyl esters of lower monocarboxylic acids on the micro-scale [157] is based on the same reaction scheme. A 10-pl volume of an ethanolic solution of carboxylic acids (ca. 1 pg/pl)... 

Another method involves the use of an Emlch filter stick fitted through a rubber stopper into a thick-walled suction tube the filtrate is collected in a micro test-tube (Fig. 11.51). The filter stick has a small pad of purified asbestos above the constriction. 

Another option is the aseptic processing, which involves a series of aseptic steps. Each of them must be highly controlled since the introduction of micro-organisms must be avoided all along the process. Aseptic filtration or aseptic processes are time-consuming, expensive, difficult to monitor and the SAL value is limited to 10 -10 , so alternative methods for sterilization of thermosensitive solid drugs are needed. 

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