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A variety of porous membrane materials are available for filtration of solutions which selectively retain large biomacromolecules. The solution can be forced through these membranes under pressure which results in concentration of the protein/DNA molecules since solvents passes freely through the membrane while protein/DNA does not.

Why should I use UF instead of dialysis? (Advantages) 1.UF is far gentler to solutes than non-membrane-based processes such as precipitation or lyophilization. 2. It is easier, faster, and higher yielding than dialysis. 3.UF is more efficient because it can simultaneously concentrate and desalt solutes. 4.There is no phase change, which often denatures labile species 5.you can perform UF at room temperature or in a cold room or refrigerated centrifuge.

1- Nitrocellulose Filters Nitrocellulose have adsorptive properties which enable them to bind particular macromolecules like proteins. Because of both the small pore size and the surface tension, liquids don ’ t easily pass through these filters with gravity as the driving force so that pressure or suction is usually employed.

The pores of the filter are not circular but irregularly shaped and account for roughly 80% of the surface area. The range of maximum particles size passed is from 0.01  m to 14  m. The most commonly used filter has a pore size of approximately 0.45  m. 1- Nitrocellulose Filters

Vacuum Filtration

Nitrocellulose is soluble in a variety of solvents and attacked by certain chemicals. Manufacturers supply similar membrane filters of cellulose acetate, nylon, Teflon and poly vinyl chloride for use in certain solvents systems. Disadvantage of nitrocellulose

They consist of a network of fine glass fibers. They are relatively thick- approximately 0.25mm Advantages: 1.They have a very high flow rate (120 ml min cm ) 2.Great capacity 3.Resistance to almost all solvents 4.Ability to be heated to high temperature for rapid drying 5.Low cost 2.Fiberglass filters

1.There is not an absolute pore size as there is with a membrane filters. 2.Sometimes tiny pieces of glass fiber are found in the filtrate Disadvantages of Fiberglass filters:

1. Clarifications of solutions: It is necessary to remove particular matter from a liquid, such as bacteria, dust, and fine precipitates (chemical and biological applications). 2.Collection of precipitates for counting radioactivity. 3. Media transfer for growing bacteria: to change the media of growing bacteria quickly 3- Applications of Filtration and Fiberglass filters

4. Nitrocellulose Filters in Binding Assay  Nitrocellulose filters bind proteins and single- stranded DNA under certain conditions.  This binds can be used as a bases for a large number of enzymatic and physicochemical assays and as a means of purifications of various materials.

1.Purification of circular DNA: Some strains of bacteria and some animal cells contain circular double stranded DNA molecules. Usually circular DNA is just a small fraction of the total DNA in an organism or cell.  The use of these binding properties is best seen by the following examples:

Antibodies are proteins and therefore bind to membrane filters. Many antigens are small organic molecules that don’t bind to nitrocellulose filters. Antigen bind to nitrocellulose only when it makes a complex with antibody( Ag-Ab)