Buffer solutions:
Buffer solutions are solutions of compounds or mixtures of compounds which resist change in their pH upon addition of small quantities of an acid or alkali.
Buffer action:
The ability of certain solutions to resist change in their pH upon addition of an acid or a base is known as the “Buffer action”
Buffer capacity:
The buffer capacity of a solution is a measure of its magnitude of resistance to change in pH on addition of an acid or base. It is also referred to as buffer index, buffer efficiency, buffer coefficient or buffer value.
ΔΒ
β = --------------
ΔpH
β = Buffer Capacity
ΔΒ = Small increment in gram equivalent
per liter of strong base (or acid).
ΔpH = Small change of pH.
Factors affecting pH of Buffer Solutions:-
The pH of a buffer solution may be affected by
Ø Fluctuation in the temperature
Ø Its dilution with a solvent.
Ø The addition of a neutral salt.
Biological buffers:
Ø The pH of blood is maintained at about 7.4 with a range of 7.0 to 8.0.
Ø The pH of lacrimal fluid or tears is about 7.4 with a range of 7.0 to 8.0. Tears degree of buffer capacity with pH value between 3.5 and 10.5 can usually be tolerated with little discomfort.
Ø The average pH of urine is about 6.0 with a range of 4.5 to 7.8.
Pharmaceutical Buffers:
1. Buffers in tablet formulation:-
Ø Sodium bicarbonate
Ø Magnesium carbonate
Ø Sodium citrate
2. Buffers in ophthalmic preparation:-
Ø Clude borate
Ø Phosphate and carbonate buffers.
3. Buffers in parenteral preparations:-
Ø Acetate buffers
Ø Phosphate buffers
Ø Citrate buffers
Ø Glutamate buffers
4. Buffers in creams and ointments:-
Ø Citric acid and its salts.
Ø Phosphoric acid and its salts.
