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(dīăl`ĭsĭs), in chemistry, transfer of solute (dissolved solids) across a semipermeable membrane. Strictly speaking, dialysis refers only to the transfer of the solute; transfer of the solvent is called osmosisosmosis
, transfer of a liquid solvent through a semipermeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to transfer of solvent; transfer of solute is called dialysis.
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. Dialysis is frequently used to separate different components of a solution. For example, a solution of starch and sodium chloride in water can be separated by placing the mixture in a vessel on one side of a semipermeable membrane and placing pure water on the other side. The smaller particles of sodium chloride (which dissolve in water to form sodium and chloride ions) will diffuse across the membrane; diffusion of the much larger starch particles (which are not truly in solution but are in colloidal suspension) is hindered and may be completely prevented. By continuously or periodically replacing the solvent with fresh solvent, almost all of the sodium chloride can be removed. The method was originated by Thomas Graham, who termed the substance that remained within the membrane a colloid and the substance that diffused a crystalloid.

An extension of the method makes possible the separation of mixed colloids by the use of a semipermeable membrane (usually synthetic) of known selectivity, i.e., one that will permit the diffusion of one colloid and hinder the diffusion of others. Mixed macromolecules, such as proteins, may be similarly separated. By the use of graded semipermeable membranes chosen to allow successively smaller molecules to pass, mixtures can be separated into components of graded ranges of molecular weight.


Artificial kidney machines have been developed that make use of dialysis to purify the blood of persons whose kidneys have ceased to function. Known as hemodialysis, this procedure has saved the lives of many persons suffering from renal failure. In such machines, blood is circulated on one side of a semipermeable membrane (often cellophane) while a special dialysis fluid is circulated on the other side. The dialysis fluid must be a solution that closely matches the chemical composition of the blood. Metabolic waste products such as urea and creatinine diffuse through the membrane into the dialysis fluid and are discarded, while loss by diffusion of substances necessary to the body (such as sodium chloride) is prevented by their presence in the dialysis fluid.

In peritoneal hemodialysis, the dialysis fluid is introduced into the abdominal cavity. Waste products leach from the blood vessels into the fluid, which is later drained from the patient. Home peritoneal dialysis machines that release patients from dependence on hospital dialysis (usually three 4-hr visits weekly) have been available since the 1980s. See diffusiondiffusion,
in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life processes.
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the removal of impurities of low-molecular-weight substances from colloidal systems and solutions of macromolecular compounds by means of semipermeable membranes, or partitions, which pass small molecules and ions but hold back colloidal particles and macromolecules.

The simplest device for dialysis, a dialyzer, is a pouch or sleeve made of semipermeable material that is filled with the liquid to be purified and immersed in a solvent (a dispersion medium). Cylindrical vessels with a semipermeable membrane instead of a bottom are often used in place of a pouch. The membranes are made of collodion, cellophane, animal and plant membranes, and synthetic materials. Diffusion processes are the basis of dialysis; therefore, it proceeds very slowly. Dialysis may be accelerated by increasing the ratio of the membrane area to the volume of the liquid to be dialyzed, by increasing the temperature, by agitation, by creating a pressure difference across the membrane, and by frequent or continuous replacement of the solvent into which the ions or molecules of the low-molecular-weight substance pass (diffuse) through the membrane.

Dialysis in an electric field (electrodialysis) accelerates the removal of electrolytes from dialyzed systems by dozens of times. A simple electrodialyzer consists of three chambers separated by membranes. The liquid to be purified is poured into the central chamber, and electrodes immersed in solvent are located in the side flow chambers. The ions in the stationary electrical field move directly to the corresponding electrodes, penetrating the membrane from the central chamber into the side chambers. Electrodialysis is particularly efficient when ionite membranes made of ion-exchange materials are used. Depending on the sign of the electrical charge on their surface, the membranes pass either cations or anions. Multichamber electrodialyzers with ionite membranes are used in hydrometallurgy, in the atomic industry (to treat effluents, concentrate saline solutions, and separate elements close in properties), and in the desalinization of seawater.

Dialysis and electrodialysis are used in many industrial processes, in physicochemical and biological research, and in medicine. The dialysis method, which was called vivi-diffusion, was used in 1913 by the American scientist D. Abel to study the components of the blood of a living organism. The animal’s blood passed from an artery into a vein through colloidal tubes placed in a glass cylinder filled with physiologic solution. Abel’s unit was the basis for the design of the artificial kidney, which is used for hemodialysis.


Voiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964.
Elektrokineticheskie svoistva kapilliarnykh sistem. Moscow-Leningrad, 1956.
Perry, J. H. Spravochnik inzhenera-khimika, vol. 1. Leningrad, 1969. Page 624. (Translated from English.)
Demineralizatsiia metodom elektrodializa (ionitovye membrany). Moscow, 1963. (Translated from English.)


(physical chemistry)
A process of selective diffusion through a membrane; usually used to separate low-molecular-weight solutes which diffuse through the membrane from the colloidal and high-molecular-weight solutes which do not.


1. the separation of small molecules from large molecules and colloids in a solution by the selective diffusion of the small molecules through a semipermeable membrane
References in periodicals archive ?
Les traitements sont peu nombreux, et l'evolution de la maladie necessite frequemment le recours a la dialyse ou a la transplantation.
Mandatory variant concerns the provision of generators against the provision of associated disposables (kits and cartridges) based on 10,000 dialyses per year for 5 years.
The rapid increase in incidence of renal failure and dialyses make it necessary for dental practitioners to thoroughly understand the special treatment need and considerations for such patient.16 The aim of this study was to investigate and study the oral health status and the level of periodontal and dental health in patients on renal dialyses in Jordanian population.
Le deuxieme article s'intitule * Understanding the lived experience of loss and grieving in persons with end-stage renal disease: A humanbecoming approach *Comprendre l'experience de perte et de deuil vecue par les personnes atteintes d'insuffisance renale terminale: Une approche de la theorie de l'humain en devenir], par Jennifer Duteau, chef de pratique clinique, Nephrologie et dialyse, au Humber River Regional Hospital, a Weston, en Ontario.
In addition, fewer recipients in the treatment group (24.7%) needed multiple dialyses before renal function recovered than did recipients in the nondopamine group (35.4%).
He is really sick now as both his kidneys have failed and he is undergoing three dialyses a week without which he won't survive."
He concluded that, for this reason, the patient was entitled to receive dialysis on a regular schedule but that repeated emergency dialyses, after skipping one or more treatments, were not warranted.
'Today the SIUT is performing some 850 dialyses every day,' he said.
The Hospital spread over an area of 32 kanals with a constructed area of 84,600 sq feet shall have a diagnostic, O.P.D., Male and Female Wards, operation theatre, dialyses unit and other facilities.
Aurons - nous les moyens de faire face a ce flux de malades qui devront etre dialyses ?
La dialyse: une solution palliative Pour permettre de faire face a la grande demande de dialyse et pour que les malades n'aient plus a attendre pour beneficier des seances de dialyse, le ministere de la Sante a sous traite depuis 2008 ce service aupres de certains centres de dialyses du secteur prive afin de repondre a la demande actuelle de dialyse, ce qui a permis a des patients indigents d'etre traites.
Secretary Health listen the problems of the patients and assured that Health Department would provide 11 extra dialyses machines for the centre by the end of June, 2010.