This document discusses buffer capacity, preparation, and stability. It defines buffer capacity as the strength to resist pH changes when acid or base is added. Greater buffer capacity means a buffer can tolerate more added acid/base before pH changes. The document provides equations to calculate buffer capacity more exactly. It also discusses how buffers are prepared by combining a weak acid and its salt, or weak base and its salt. Examples like phosphate buffer are given. Finally, it outlines factors that impact buffer stability like proper storage, temperature, and protection from light and microbes. Buffers should maintain pH and not degrade over their typical 1-2 year shelf life.

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