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Biological and Pharmaceutical applications of buffers
Applications of Buffers- Biological and Pharmaceutical applications of Buffrer
Applications of Buffers in Pharmaceutical systems
i) Solid Dosage Forms
Buffers are used in solid dosage forms such as tablets, capsules and powders for controlling the pH of the environment around the solid particles. This has practical application with the drugs that have dissolution rate limited absorption from unbuffered solutions..
One of the special applications of buffers is to reduce the gastric irritation caused by the acidic drugs. For example, sodium bicarbonate, magnesium carbonate and sodium citrate antacids are used for the purpose of reducing acidity.
ii) Semisolid Dosage Forms
Semisolid preparations such as creams and ointments undergo pH changes upon storage for a long time, resulting in its reduced stability.Hence buffers such as citric acid and sodium citrate or phosphoric acid/sodium phosphate are used in these preparations so as to maintain their stability.
iii) Parenteral Products
Use of buffers is common in the parenteral products.Change in pH to the higher side (more than 10) may cause tissue necrosis while on the lower side (below 3) it may cause pain at the site of action.So pH should be adjusted. Commonly used buffers include citrate, glutamate, phthalate and acetate. The pH optimization is generally carried out to have better solubility, stability and reduced irritancy of the product.
iv) Ophthalmic Products
The purpose of buffering some ophthalmic solution is to prevent an increase in pH that can affect both the solubility and the stability of the drug. The decision whether or not buffering agents should be added in preparing an ophthalmic solution is based on several considerations. Normal tears have a pH of about 7.4 and possess some buffer capacity.
Applications of buffers in Biological systems
Buffers for biological systems should satisfy the following requirements
- A pKa value between 6.0 to 8.0
- High water solubility and minimal organic solvent solubility
- Exclusion by cellular membranes
- Minimal interaction between buffer and critical reaction compounds
- Should not absorb light in the visible and UV spectrum
- Stable and resistant to enzymatic degradation
- Minimal changes on dissociation from changes in Concentration and temperature
- Easy to manufacture and purify
- Cost effective
- Ionic strength
- Permeability
Buffers are important to biological systems because they enable the organism to maintain homeostasis with little physiological cost.
Blood
Blood consists of primary and secondary buffer systems contributing the pH 7.4.When pH of the blood goes below 7.0 or above 7.8, life is in danger .
The pH of the blood in diabetic coma can to drop as low as 6.8.
Primary buffers present in plasma are – Carbonic acid-bicarbonate system and acid alkali salts of phosphoric acid systems.
Secondary buffers that are present in erythrocytes are – hemoglobin/ oxyhemoglobin system and acid salts of phosphoric acid system.
Lacrimal Fluids
Lacrimal fluids (tears) have a great degree of buffer capacity, allowing dilution of 1:15 with neutral distilled water. The pH of tears is about 7.4 , with a range of 7.0 to 8.0. Normally, pure conjunctival fluid is more acidic than the tear fluids commonly employed in pharmacy. The pH increase rapidly when the sample is removed for analysis because of loss of carbon dioxide from the tear fluid.
Three Buffer Systems in Body Fluid
Protein Buffer Systems
Proteins are the most important and widely operating buffers in the body fluid. The protein buffer system is an integral component of the body’s pH controlling mechanism. Protein buffers are either intracellular or extracellular.
Their functionality is mainly intracellular focused and include haemoglobin (Hb). Hb is the protein that functions to transport oxygen within the body. Plasma proteins function as buffers but their amount is small in comparison with the intracellular protein buffers. Protein buffers include basic groups, and acidic protein buffer groups, that act as hydrogen ion depletors or donors to maintain the pH level at 7.4.
Phosphate Buffer System
The phosphate buffer system consists of two ions: hydrogen phosphate ions and dihydrogen phosphate ions. The pH level of the blood drops below 7.4 when the H+ ions in the bloodstream increase.
Hydrogen phosphate ions accept all additional H+ ions to reestablish the equilibrium between the hydroxide and hydrogen ions in the blood. When the pH level of the blood increases above 7.4, the dihydrogen phosphate ions release additional hydrogen ions to reinstate the pH level of the blood to its optimal 7.4.
Bicarbonate Buffer System
The bicarbonate buffer system functions to maintain the pH level in the blood of mammals. It also plays a major role in the formation of acid in the stomach, and to neutralise the pH of chyme that enters the small intestine from the stomach. The bicarbonate buffer system manages acid/base imbalances and effectively manages the release of excess carbon dioxide as a bi-product of cellular respiration.
Not to mention there are many more biological and pharmaceutical applications of buffers.
Buffer Capacity
Buffering capacity is defined as the number of moles of strong base or acid needed to change the pH of a litre of buffer solution by one unit. A general buffer capacity estimate is 40 percent of the total sum of the molarities of the conjugate base and acid.
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Written by Uma Maheswari P