ULTRAFILTRATION — a kind of membrane filtering, i.e. process of fractionation by the size of the dissolved or suspended components by filtering through membranes with finite permeability. At. finds broad application in virology (see), microbiology (see) and others medical - biol. sciences, and also in the medical and food industry.
At At. solvent and the components dissolved or suspended in it with particle sizes, smaller, than diameter of a time of a membrane of the filter, under the influence of excessive pressure from above, exhaustions from below (see) pass pl of acceleration during the centrifuging through the filter, and larger components accumulate over it. Depending on pore size distinguish ultrafilters (diameter of a time from 0.001 to 0,05 microns) and microporous filters (diameter of a time from 0,05 microns and more). Ultrafilters use for concoction, fractionation and desalting of solutions of proteins and other organic and inorganic polymers about a pier. it is powerful (weighing) 500 — 300 000, and also for concoction of viruses (see). Microporous filters apply to fractionation and concoction of various suspensions (see) and to sterilization (see) liquids. Sovr. ultrafilters usually represent the dense anisotropic (leathery) membranes from inert polymers placed on high-porous substrates and have the form of the disks, cones or hollow fibers collected in a plait. Use homogeneous cellulose filters less often. Microporous filters make also of glass and ceramics. Broad use in microbiology ceramic filters in the form of cylinders had, so-called candles of Shamberlan (see. Bacterial filters).
56 At JITRAFI LTRATSIYA
Existence of positive or negative pressure distinguishes At. from dialysis (see), to-rogo usual diffusion is the cornerstone (see), and the direction of motion of the molecules of solvent and the fine dissolved particles is defined by a gradient of concentration on both sides of a semipermeable membrane. However at At., as well as at dialysis, process is not followed by increase in concentration of low-molecular substances and increase in ionic strength of solution. The important characteristic of ultrafilters which is often defining a possibility of use At. for the solution of this or that experimental or production task, their productivity, i.e. the speed of current of the filtered liquid via the ultrafilter expressed usually in ml/min./cm2 is. With other things being equal the size of productivity of the ultrafilter increases with increase in diameter of a time and their number per acre of the filter (degree of porosity), reduction of thickness of the ultrafilter and increase of the created difference of pressure. However its productivity specified in the passport of the ultrafilter is established usually at absolutely pure filtering. This operation gives the chance to determine by filtration rate porosity of a membrane of the filter since the amount of water passing for a unit of time with a certain pressure through 1 cm2 of the ultrafilter, in direct ratio to a square of a diakhmetr of its time. It should be noted that at long passing via the ultrafilter of a usual distilled water eventually there occurs reduction of filter capacity. During the filtering biol. liquids, virus and microbic suspensions reduction of filter capacity occurs much quicker. Decline in production of the ultrafilter is explained by three main reasons: primary adsorption (see), i.e. molecular and ionic adsorption of particles on the surface of the ultrafilter and in its time that leads to reduction of their diameter; so-called blocking or kolmatazhy — a mechanical delay of the filtered particles and especially their units in a time of the ultrafilter that leads to clogging of a time and reduction of degree of porosity of the filter; a mechanical delay of more coarse particles on the surface of the filter therefore the layer closing a working surface of the ultrafilter and badly passable or absolutely impassable for liquid is formed. The surface of a time on 1 cm2 of the best membrane ultrafilters reaches 50 — 100 zh2 that can cause adsorption of 50 — 500 mg of protein in the form of a monolayer. Ionic adsorption on the ultrafilter depends on the size of a charge of material, from to-rogo the ultrafilter is made. Ionic and molecular adsorption in addition to delay of straining action can cause considerable losses of target material also. Primary adsorption on the ultrafilter, as a rule, decreases at increase in a difference of pressure on both sides of a membrane thanks to so-called effect of blowing off of an adsorbed layer. Such reception, however, does not help to eliminate blocking of a time, and the positive effect in this case is reached only by addition of surfactants (see Detergents). Formation of badly permeable surface layer of ballast substances can be slowed down or prevented by preliminary removal of these substances, and also use of prefilters — filters with a large diameter of the time imposed on the ultrafilter or creation of current of the filtered liquid parallel to the surface of the ultrafilter.
Distinguish conservative, or static, ways U., at to-rykh the filtered liquid moves via the ultrafilter perpendicular to its working surface towards more low pressure, and also flowing ways U., at to-rykh the filtered liquid along with the described movement through a working surface of the ultrafilter moves also parallel to this surface. Flowing ultrafilters at industrial use combine in the whole batteries, at the same time their total working surface can reach several thousand sq.m. At large volumes of the filtered solutions filtering kakhmer can connect to filters and prefilters in parallel or consistently in batteries from 5 — 10 filtering elements. Excessive pressure in the camera is created both at the expense of vacuum in the receiver, and due to operation of the pump giving liquid from a tank to the camera. Thanks to operation of the pump the amount of the liquid coming to the camera surpasses its expense due to filtering therefore in the camera the reversed current of the liquid which is partially returned to the tank directed parallel to the surface of the filter is created. This fluid movement does minimum formation of badly passable surface layer of ballast substances.
In a lab. conditions flowing filtering is carried out by means of fiber ultrafilters. At the same time the concentrated solution circulates in hollow fibers of the filter, and the filtrate gathers outside.
Two options of use of ultrafilters are known. At the first of them the particles interesting the researcher and macromolecules pass through the ultrafilter, and larger linger on it. Such way provides cleaning and fractionation of suspension of particles by the size, and also sterilization of the filtered solution in case of bacterial pollution, but not its concoction. At the second way the particles interesting the researcher or macromolecules surpass diameter of a time of the ultrafilter therefore concoction and cleaning, but not sterilization is reached them in the sizes.
In view of a huge surface of a time in ultrafilters the last quite often use for adsorption from solution of macromolecules and viruses with their subsequent eluating. Rastvorikhmy ultrafilters are in this respect convenient, after dissolution to-rykh adsorbate passes into solution.
Range of application At. in biology and medicine it is very extensive. In microbiology, virology, and also in the food industry At. apply to sterilization of solutions and suspensions, cleaning of fagolizat and virus suspensions of cells and cellular fragments. By means of membrane ultrafilters carry out concoction and cleaning of viruses and different macromolecules as in laboratory, and commercially. At. even more often use at preparation of virus and subvirus vaccines. E.g., on the standard filtering equipment of illi M a horn with the general surface of batteries of ultrafilters 2720 of sq.m process 150-liter portions of suspension of a virus of a foot-and-mouth disease (after chloroformic deproteinization) for 130 hours at 5 °; at the same time remains apprx. 90% of infectivity of a virus, it concentrates by 150 times, from solution is removed to 92% of ballast protein. At. began to use widely also in biochemistry, molecular biology, virology, microbiology, etc. at different carrying out researches using radionuclides, napr, during the determination of radioactivity of nucleic acids (see), in experiments on hybridization of DNA — DNA and RNA — DNA. Though in limited scales, but size discrimination of viruses, proteins and other macromolecules with the help continues to be applied At. Thanking At. all basic groups of the known viruses were open (see): viruses of plants and animals, oncogenous viruses (see) and bacteriophages (see). Long time At. remained the only way of cleaning of viruses (virus suspensions).
In medicine began to use the conic ultrafilters allowing with the help a lab. centrifuges to concentrate proteins of cerebrospinal and synovial liquids, proteins of urine, etc. for the subsequent analysis.
See also Filtering. Bibliography: Tikhonenko to T. I. Ma
todichesky fundamentals of biochemistry of viruses, M., 1973; Tovarnitsky V. I. both Glukharev of G. P. Ultrafiltra and ultrafiltration, M., 1951;
Stroh-maier K. Virus concentration by ultrafiltration, in book: Meth. in virol., ed. by K. Maramorosch a. H. Koprowski, v. 2, p. 245, N. Y. — L., 1967. T. I. Tikhonenko.