BUFFERS AND BUFFER SOLUTIONS
%20(21).jpeg)
.png)
The presence of certain substances or combinations of substances in aqueous solution imparts to the system the ability to maintain a desired pH at a relatively constant level, even with the addition of materials that may change [H+].
These substances or combinations of substances are called buffers.
These substances or combinations of substances are called buffers.
Their ability to resist changes in pH is referred to as buffer action.
Their efficiency is measured by the function known as buffer capacity. Solutions of them are buffer solutions.
Buffers are used to establish and maintain an ion activity within rather narrow limits
In pharmacy, the most common buffer systems are used in:
1. The preparation of such DFs(Drug Formation) as injections & ophthalmic solutions, which are placed directly into pH sensitive body fluids.
2. The manufacture of formulations in w/c the pH must be maintained at a constant relative level to ensure maximum product stability.
3. Pharmaceutical tests and assays requiring adjustment to or maintenance of a specific pH for analytic purposes.
A buffer solution is usually composed of a weak acid and a salt of the acid, such as acetic acid and sodium acetate, or a weak base and a salt of the base, such as ammonium hydroxide & ammonium chloride.
Typical buffer systems that may be used in pharmaceutical formulations include the following pairs:
Their efficiency is measured by the function known as buffer capacity. Solutions of them are buffer solutions.
Buffers are used to establish and maintain an ion activity within rather narrow limits
In pharmacy, the most common buffer systems are used in:
1. The preparation of such DFs(Drug Formation) as injections & ophthalmic solutions, which are placed directly into pH sensitive body fluids.
2. The manufacture of formulations in w/c the pH must be maintained at a constant relative level to ensure maximum product stability.
3. Pharmaceutical tests and assays requiring adjustment to or maintenance of a specific pH for analytic purposes.
A buffer solution is usually composed of a weak acid and a salt of the acid, such as acetic acid and sodium acetate, or a weak base and a salt of the base, such as ammonium hydroxide & ammonium chloride.
Typical buffer systems that may be used in pharmaceutical formulations include the following pairs:
- Acetic acid and sodium acetate
- Aoric acid and sodium borate
- Disodium phosphate and sodium acid phosphate
Formulas for standard buffer solutions for pharmaceutical analysis are given in the United States Pharmacopeia (USP).
In the selection of a buffer system, due consideration must be given to the dissociation constant of the weak acid or base to ensure maximum buffer capacity.
This dissociation constant, in the case of an acid, is a measure of the strength of the acid
The more readily the acid dissociates, the higher its dissociation constant and the stronger the acid.
The dissociation constant, or Ka value, of a weak acid is given by the equation:
Ka = (H+) (A-)
In the selection of a buffer system, due consideration must be given to the dissociation constant of the weak acid or base to ensure maximum buffer capacity.
This dissociation constant, in the case of an acid, is a measure of the strength of the acid
The more readily the acid dissociates, the higher its dissociation constant and the stronger the acid.
The dissociation constant, or Ka value, of a weak acid is given by the equation:
Ka = (H+) (A-)
(HA)
From this we can determine the PH
PH = Pka + log (salt/acid)
It's the Henderson-Hasselbalch equation for weak acids, commonly known as the buffer equation
We can similarly calculate the dissociation constant, or Kb value, of a weak base and then determine the POH:
Kb = (B+)(OH-)
From this we can determine the PH
PH = Pka + log (salt/acid)
It's the Henderson-Hasselbalch equation for weak acids, commonly known as the buffer equation
We can similarly calculate the dissociation constant, or Kb value, of a weak base and then determine the POH:
Kb = (B+)(OH-)
(BOH)
Then, POH= Pkb+ log (salt/base)
The buffer equation for weak bases, which is derived from this relationship, may be expressed as:
PH = PKW-PKb+ log (base/salt)
The buffer equation is useful for calculating
The pH of a buffer system if its composition is know
The molar ratio of the components of a buffer system required to give a solution of a desired PH
The equation can also be used to calculate the change in pH of a buffered solution with the addition of a given amount of acid or base.
Then, POH= Pkb+ log (salt/base)
The buffer equation for weak bases, which is derived from this relationship, may be expressed as:
PH = PKW-PKb+ log (base/salt)
The buffer equation is useful for calculating
The pH of a buffer system if its composition is know
The molar ratio of the components of a buffer system required to give a solution of a desired PH
The equation can also be used to calculate the change in pH of a buffered solution with the addition of a given amount of acid or base.
More Information