Submitted by : D.Sairam
Course Instructor : Dr. Subhabrata Kar
Course : Bioanalytical and
Course Code: BSBT 202
Presentation Code: U2P2
Principle of Dialysis
Preparation of Dialysis membranes
Characteristics of Regenerated Cellulose Membrane
Applications of Dialysis
• Dialysis comes from two Greek words namely ‘Dia” and “Lysis” meaning
splitting or separating materials through a membrane
• Earliest Dialysis was carried out of Crystalloids using Albumin coated
• Today Dialysis ( reference to medical dialysis) has become a life saving
technique that is widely used all over the world.
• Dialysis is the process of separating molecules in solution by the difference in their
rates of diffusion through a semipermeable membrane.
• In dialysis, a sample and a buffer solution (called the dialysate) are separated by a
semi-permeable membrane that causes different diffusion rates, thereby permitting
the separation of molecules in both the sample and dialysate.
• It is due to the pore size of the membrane that large molecules in the sample cannot
pass through the membrane, thereby restricting their diffusion from the sample
• Once equilibrium is reached, the final concentration of molecules is dependent on
the volumes of the solutions involved, and if the equilibrated dialysate is replaced (or
exchanged) with fresh dialysate (see procedure below), diffusion will further reduce
the concentration of the small molecules in the sample.
• If the equilibrated dialysate is replaced (or exchanged) with fresh dialysate (see
procedure below), diffusion will further reduce the concentration of the small
molecules in the sample.
Principle of Dialysis
• The Molecular-Weight cut-off (MWCO) parameters characterize
• Membranes with MWCOs ranging from1-100,000 kDa are
commercially available, membranes with MWCOs near 10 kDa are most
• MWCO refers to the smallest average molecular mass of a standard
molecule that will not effectively diffuse across the membrane during
• Molecules near the MMCO value will diffuse very slowly so this shows
the importance of choosing an appropriate membrane.
• Ideally a molecule must be at least 20- to 50-times smaller than the
MWCO rating of a membrane to allow smooth diffusion.
• Dialysis membranes for laboratory use are typically made of a film of
regenerated cellulose or cellulose esters
Preparation of Dialysis Membrane
• Membranes ( used in Laboratory Dialysis) are generally are made up of
• Glycerol is frequently added as a humectant to prevent cracking during
drying and to help maintain desired pore structure
• Pores range from 15-50 Angstroms for 3.5K, 7K and 10K MWCO
• Regenerated cellulose is hydrophilic and easily saturated in buffer to
provide a homogeneous medium for dialysis in aqueous solutes
• Membrane contaminants include sulfur compounds (0.01-0.3%), heavy
metals (trace) and glycerol (0-21%).
• Most of these small compounds diffuse out of the membrane during the
dialysis process> Solution: pre-dialysis
Characteristics of Regenerated Cellulose membrane
• It is an economical material that is best suited for applications where
particles ( significantly large) are separated on the basis of their size.
• It is chemically stable in most conditions.
• It can be used with dilute strong acids and bases, concentrated weak
acids and bases.
• It can tolerate pH 2 - 12 and temperatures 4 - 121 °C.
• However, Biotech Grade Dialysis Membranes are preferred for
processes that involve higher membrane purity and better selectivity
Applications of Dialysis
• The applications of Dialysis are far and varied. The following is a
compilation of a few of them:
• Haemodialysis: Removal of salts, creatinine from blood in case of
• Micro dialysis: Removal of extracellular fluid, hormones for analysis
and to determine their concentrations in the body.
• Electrodialysis (ED): It is used to transport salt ions from
one solution through ion-exchange membranes to another solution
under the influence of an applied electric potential difference.
• Peritoneal Dialysis (PD): It uses the patient's peritoneum (in
the abdomen ) as a membrane across which fluids and dissolved
substances (urea, glucose, albumin and molecules) are exchanged from
Source: National Kidney
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