BUFFER CAPACITY PREPARATION OF BUFFER STABILITY OF BUFFER

1. BUFFER CAPACITY
PREPARATION OF BUFFER
STABILITY OF BUFFER
BY
PROF. TAUFIK MULLA
DEPT. OF PHARMACEUTICS
SPBC COLLEGE OF PHARMACY

2. • Buffer solution do not change pH by addition of strong acid / strong base.
• Buffering action is determined in terms of buffer capacity.
• Definition = the strength or capacity to resist changes in pH of system by addition of acid or base known as buffer
capacity.
• Capacity of buffer to neutralize external acid is equal to amount of base present in buffer.
• Maximum amount of base added is equal to amount of weak acid present in buffer.
dn
buffer capacity ß = _____
dpH
n= gram equivalent of added strong acid or base added to 1L buffer
dpH= pH change caused by addition of strong acid or base
• Greater buffer capacity , better is the buffer as it can tolerate more acid or base without changes in pH.

3. • A buffer solution can resist a small amount of change of pH on adding acid or alkali to the
solution. Buffer capacities ranging from 0.01-0.1 are usually adequate for most pharmaceutical
solutions.
• In 1922, Van Slyke first introduced an approximate equation to determine the buffer capacity by
the following equation:
• β = Buffer capacity
• delta Δ= finite change
• ΔB =the small increment in gram equivalents (gEq)/litre of strong base added to the buffer
solution to produce a pH change of ΔpH.
• According to equation, the buffer capacity of a solution has a value of 1 when the addition of 1 g
Eq of strong base (or acid) to 1 litre of the buffer solution results in a change of 1 pH unit.
• The higher the buffer capacity the less the buffer solution changes its pH.

4. • A more exact equation for buffer capacity: The buffer capacity calculated from above equation
is only approximate. It gives the average buffer capacity over the increment of base added.
• Koppel and Spiro and Van Slyke developed a more exact equation,
• Where, C = the total buffer concentration (i.e. the sum of the molar concentrations of acid and
• salt).
• K = dissociation constant
• Acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is
a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a
chemical reaction
• H3O = hydrogen ion concentration

5. EXAMPLE:
If hydrogen ion concentration is 1.75 x 10-5, pH = 4.76 what is the capacity of the buffer containing 0.10
mole of
each of acetic acid and sodium acetate per liter of solution ?
The total concentration , C = [acid] + [salt], is 0.20 mol/l and the dissociation constant Ka is 1.75 x 10-5
β = 2.3 C Ka [H3O+]
(Ka + [H3O+])2
β = 2.3 x 0.20 x (1.75x10-5) x (1.75 X 10-5) = 0.115
[(1.75x10-5) +(1.75 X 10-5)]2

6. PREPARATION OF BUFFER
• A buffer solution prepared as a combination of weak acid and their salt or weak base and its salt.
• Criteria for Good Buffer :
• Non toxic to cell / tissue
• Having pH range between 6-8
• Reduced ion effect
• Maximum solubility in water
• Do not affect stability by ionic composition and temperature
• Composition of buffer easy to obtain and prepared
• While making buffer solution, we add storng acid (HCl) to reduced pH of acidic buffer and strong base
(NaOH) to reduced pH of basic buffer
• Fluid present in cell or out of cell or inbetween cell have specific constant pH so to preserve or to
maintain that pH we use buffer solution.

7. • Buffer solution are generally available in the form of powder or tablet or liquid in variety of
pH.
• Example of buffer solution :
• Phosphate Buffer – potassium dihydrogen phosphate solution 50ml placed in 200ml volumetric
flask and specified volume of sodium hydroxide (3.9 to 43.7 ml) added to adjust pH 8-10 and lastly
water is added to maintain volume.
• Acidic buffer
• Basic buffer
• Acetic acid buffer solution

8. STABILITY OF BUFFER
• Shelf life of marketed buffer is 2 yrs.
• 3 – 6 months for open buffer having pH less than 8
• Basic buffer may change their pH value when it come in contact to carbon dioxide in air. CO2 from air dissolve and form
carbonic acid which decrease pH of solution.
• Shelf life of basic buffer is 1 month (if it open)
• Whenever we are preparing buffer solution we need to label on it the exact date of manufacturing and also need to label
the initial pH of the solution.
• Stored in tightly closed container it sealed it. Air tight bottle.
• pH of buffer usually done at 25 C temp. if buffer solution stored in low temp then prior use need to placed in room temp.
• Do not store buffer solution near window or near heat source.
• Some buffer stored in amber colored bottle to protect it from sun light.
• Buffer must be stable and do not break during storage.
• Should not oxidized
• Do not affect by the component in which buffer is used
• should not support growth of micro organism during storage