Micro filtration

High-pressure homogenization, bead mills, sonication, enzymatic treatments Filtration (micro-, ultra-, nano-filtration), precipitation, solvent extraction, ion exchange, size exclusion, affinity chromatography Hydrophobic interaction/reversed-phase chromatography... 

A Pyrex micro filter (Fig. XII, 2, 18) of 8 ml. capacity and furnished with a sintered glass disc is useful for the filtration of hot or boihng hquids. The long cylindrical tube reduces evaporation. The filter may be inserted into a test-tube with side arm (Fig. XII, 2, 13) and the filtrate collected in a centrifuge tube or semimicro test-tube receiver. 

Barrier Phenomenon. In red cell filtration, the blood first comes into contact with a screen filter. This screen filter, generally a 7—10-) m filter, does not allow micro aggregate debris through. As the blood product passes through the deeper layer of the filter, the barrier phenomenon continues as the fiber density increases. As the path becomes more and more tortuous the cells are more likely to be trapped in the filter. 

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. 

White, D.A., Assabumrungrat, S., Puttick, S., Sizing of inorganic micro filtration monoliths for water and air purification, Trans.of the IChemE, V.73B, pp. 108-114, 1995. 

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The size separation of proteins has been routinely called gel filtration because of the historic use of cross-linked gels for this application. Specially modified Zorbax PSM columns, Zorbax GF-250 and Zorbax GE-450, are used for separating proteins by size. These columns are packed with porous silica micro-... 

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 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. 

Micro filtration Pressure gradient 0.1-10 xm Small particles, large colloids, microbial cells... 

Removal of solid debris using a micro-centrifuge is an alternative technique to filtration. Although it requires special apparatus, the... 

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. 

Tomisek, A. J. and Natelson, S. Fluorometric assay of ultramicro quantities of glucose with Somogyi filtrate and hexokinase. Micro-chem. J. (1974),... 

Pectin lyase (PNL) activity was measured spectrophotometrically by the increase in absorbance at 235 nm of the 4,5-unsaturated reaction products. Reaction mixtures containing 0.25 ml of culture filtrate, 0.25 ml of distilled water and 2.0 ml of 0.24% pectin from apple (Fluka) in 0.05M tris-HCl buffer (pH 8.0) with ImM CaCl2, were incubated at 37 C for 10 minutes. One unit of enzyme is defined as the amount of enzyme which forms Ipmol of 4,5-unsaturated product per minute under the conditions of the assay. The molar extinction coefficients of the unsaturated products is 5550 M cm [25]. Also viscosity measurements were made using Cannon-Fenske viscometers or Ostwald micro-viscosimeter, at 37°C. Reaction mixtures consisted of enzyme solution and 0.75% pectin in 0.05 M tris-HCl buffer (pH 8.0) with 0.5 mM CaCl2. One unit is defined as the amount of enzyme required to change the inverse specific viscosity by 0.001 min under the conditions of reaction. Specific viscosity (n p) is (t/to)-l, where t is the flow time (sec) of the reaction mixture and t is the flow time of the buffer. The inverse pecific viscosity (n p ) is proportional to the incubation time and the amount of enzyme used [26]. Units of enzyme activity were determined for 10 min of reaction. 

Because of the cost of mains water, many companies have utilised on-site boreholes as their water source. Such water, percolating through the soil, will be much more contaminated with micro-organisms than the mains supply and will require treatment before use. River or canal water will contain even more micro-organisms and, although after sand or other filtration may appear clear, it still represents a significant contamination hazard to products in which it is used. 

Membrane filtration processes, such as reverse osmosis, and micro and ultra filtration, are used to filter out dissolved solids in certain applications see Table 10.9. These specialised processes will not be discussed in this book. A comprehensive description of the techniques used and their applications is given in Volume 2, Chapter 8 see also Scott and Hughes (1995), Cheryan (1986), McGregor (1986) and Porter (1997). 

Filter the cold acetone rapidly into a glass-stoppered test tube by means of suction through a 2- or 3-ml. micro Buchner funnel, fitted with a fritted-glass plate of medium porosity. Wash the tube and funnel with 3 ml. of cold acetone and combine it with the filtrate. 

Chemical analysis. Succinoglycan, purified by micro-filtration and dialysis, was hydrolysed in 0.5M sulphuric acid at a concentration of approximately 5mg/ml for 16 hours at 95 C. Sugars and acids were determined by HPLC using Biorad HPX-87 columns. No pretreatment was required for acids analysis - detection was by measurement of UV... 

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