How Does Dialysis Work? Steps, Mechanism & Practical Applications
It is one of the most common laboratory techniques that is used to remove molecules from solutions. This principle is also used to artificially purify blood in case of kidney dysfunction. This article delves into what dialysis is, the procedure and its importance.
Dialysis - Chemical Separation
To define the scientific term, ‘dialysis’ is a process of separating molecules in particular solutions with the help of a membrane that is semipermeable known as a dialysis tube. It is a separation of dissolved ions and molecules from solid solutions. The separation of molecules takes place because there is a difference in the rate of diffusion of certain molecules in the solution.
The application of dialysis is used for the elimination of small and unwanted molecules such as salt, and large unwanted molecules such as dyes in particular solutions. It is also used in the studies of drugs and electrophoresis.
History of Dialysis
The chemical procedure of dialysis was discovered and introduced by a Scottish chemist namely Thomas Graham in the year 1868.
Graham used this technique in the separation of small molecules and large molecules in an aqueous solution. The name that he has given to those diffusible substances as crystalloids and those that would get stuck in the membrane or dialysis tube is called colloids. This process of separation is also called Graham’s Law in chemistry.
This chemical separation is an extremely rapid and spontaneous process of separating with the help of the semipermeable membrane, and the most types of membranes used in the process of dialysis are cellulose and synthetic polymer.
The Procedure of Dialysis Separation
To separate molecules, dialysis is one of the most straightforward and fast-paced chemical procedures. There is particular equipment that is required for the process of dialysis such as:
A container to keep the molecules.
A dialysis tube
Control of temperature
The Steps Involved in the Procedure of Dialysis are as Follow:
Preparation of membrane according to the instructions.
Loading the molecules into a tube or any instrument.
Placing the sample solution into the dialysis tube
Dialyzation of the sample at room temperature for around 2-3 hours.
Changing of buffer and again placing the sample for the process of dialyzation for approx 2 hours.
Importance of Dialysis
It is used for two reasons (i) for introducing new molecules in a sample solution or (ii) to remove small molecules from a sample solution because it flows smoothly in any direction of the membrane. These two reasons make dialysis an extremely important chemical procedure for various applications and scientists prefer this procedure as well.
It is also one of the chemical procedures to change the size and matrix of molecules in particular samples with the help of differentiating the sizes of molecules present inside the solution. During the process of dialysis, equilibrium is obtained in between the solution and celluloid as only small molecules can pass through the membrane or dialysis tube. Dialysis chemical separation is also used in the procedure of eliminating salt.
Osmosis helps in the smooth functioning of dialysis as the fluid moves from high to low water concentration which makes it easy to pass through the semipermeable membrane or the dialysis tube.
Ultrafiltration also helps in dialysis as it easily removes the excess fluid and small molecules in the sample solution which makes the procedure of dialysis extremely easy and fast to perform.
Types of Dialysis Chemical Separation
Diffusion Dialysis
The spontaneous and rapid type of dialysis chemical separation process. It is preferred by many scientists. Diffusion Dialysis uses AEM (Anion exchange membranes) and CEM (cation exchange membrane) which is dependent on the compounds and molecules that are to be separated.
Electrodialysis
It uses the electrical potential for the procedure of dialysis chemical separation and uses the ion-membrane as a driving force. Electrodialysis is extremely important when it comes to removing molecules from aqueous solutions.
Three other kinds of electrodialysis are commonly and widely used by scientists in laboratories worldwide. They are as follow:
Reverse Dialysis
Electro-electrodialysis
Donnan dialysis
Uses of Dialysis Chemical Separation
The Application of This Chemical Separation are as Follows:
Desalting soy sauces.
The dealcoholization of beer
Alkali waste
Aqueous solutions
Acid
Caustic soda solution
De-acidification of fruits and vegetables
Food industry for desalination
Amino acids.
Neutral and basic element groups.
Fact About Dialysis Chemical Separation
Here is the List of Facts About the Dialysis Chemical Separation. They are as Follow:
Low consumption of heat
Operates under room temperature
No operating, installing, and other costs.
Flexible and stable
Good for the environment as it doesn’t pollute it.
Conclusion
Dialysis separation is a slow procedure that is slowed by differences in particle size and diffusion rates between colloidal and crystalloid materials. But it is one of the most appreciable methods when it comes to change of solvent, analytes and chemical buffers without disrupting the nature of molecules due to any sudden change of chemical environment and hence in that regard the most beneficial.
FAQs on Dialysis in Chemistry: Definition, Process & Significance
1. What is the basic principle of dialysis in chemistry?
The basic principle of dialysis is based on the differential diffusion rates of particles of different sizes through a semipermeable membrane. Colloidal particles are too large to pass through the pores of the membrane, whereas smaller molecules and ions (impurities or crystalloids) can pass through easily. This size-based separation is the foundation of the purification process.
2. How is the process of dialysis carried out to purify a colloidal solution?
The process of dialysis involves the following steps:
The impure colloidal solution is placed inside a bag made of a semipermeable membrane, such as parchment paper or cellophane.
This bag is suspended in a container of fresh, continuously flowing water or another suitable solvent.
The small solute molecules and ions (impurities) diffuse out of the bag into the surrounding water, following the concentration gradient.
The larger colloidal particles remain trapped inside the bag, resulting in a purified colloidal solution.
3. Why is it crucial to continuously replace the outer water during dialysis?
Continuously replacing the outer water is crucial to maintain a steep concentration gradient. If the water is not replaced, it will gradually become saturated with the impurity molecules diffusing out of the dialysis bag. This would slow down and eventually stop the diffusion process, leading to incomplete purification. Fresh water ensures that the concentration of impurities outside the bag remains near zero, maximising the rate of their removal.
4. What is the main difference between chemical dialysis and medical (kidney) dialysis?
While both processes use the same principle of a semipermeable membrane for separation, their primary purpose differs. In chemistry, dialysis is used to purify colloidal solutions by removing small dissolved impurities (crystalloids). In medicine, kidney dialysis (hemodialysis) is used to filter waste products like urea and excess salts from a person's blood when their kidneys are unable to do so. Here, blood acts as the colloidal solution, and the waste products are the impurities being removed.
5. What is electrodialysis and why is it sometimes preferred over simple dialysis?
Electrodialysis is a modified and faster version of dialysis used when the impurities in the colloidal sol are ionic in nature. In this method, an electric field is applied across the dialysis setup with electrodes placed in the outer water compartment. This significantly speeds up the removal of ionic impurities, as the ions are pulled towards the oppositely charged electrodes. It is preferred over simple dialysis because the natural diffusion of ions is a very slow process, and the electric field makes the purification much more efficient and faster.
6. Can you give some real-world examples of where the dialysis technique is applied?
Dialysis is a significant technique with several applications in both laboratory and industrial settings. Key examples include:
Purification of Biomolecules: In biochemistry, it is widely used to remove salts and other small molecules from solutions of proteins, DNA, and other macromolecules.
Industrial Purification: It is used in the purification of substances like starch, glue, and artificial silk from their crude forms.
Medical Field: The most well-known application is the artificial kidney machine, which uses the principle of dialysis to purify the blood of patients with kidney failure.
7. What key properties must a membrane possess to be effective for dialysis?
To be effective for dialysis, a membrane must be selectively semipermeable. This means its pore size is meticulously controlled to achieve two things simultaneously: 1) The pores must be large enough to allow the free passage of small solvent molecules and dissolved impurities (crystalloids). 2) The pores must be small enough to effectively block the passage of the larger colloidal particles. Materials like cellophane, parchment paper, and animal bladders are commonly used because they exhibit these precise properties.
