Buffer, application of buffers, pharmaceutical buffers, buffer capacity

1. BUFFER
Presented by
Prof. Salman Baig
Asst. Prof. in Pharmaceutics

2. BUFFER
❑Buffer are the mixture of compounds that, by their presence in
solution, resist change in pH upon addition of small quantities of
acid or base
❑Resistance to change in pH is known as buffer action
❑Buffer is the combination of weak acid and its conjugate base

3. APPLICATIONS OF BUFFER
❑Used in chemical analysis and calibration (standardization) of pH
measurement system
❑Used during the chemical manufacturing and biochemical processing
❑Used in the fermentation processes
❑Used for stability of a drug in an aqueous solution. For example, ester
drugs are very susceptible to hydrolytic reactions. Buffering formulations
at proper pH can reduce the rate of hydrolysis

4. APPLICATIONS OF BUFFER
❑Buffering a formulation to near neutral pH (7.4) can reduce tissue irritation
in ophthalmic products and parenteral products
❑In parenteral preparations (i.e. injections):In case of parenteral preparations, pH
should be considered carefully as large deviations of pH may lead to serious
consequences. The ideal pH of a parenteral product is 7.4, which is pH of blood; The
commonly used buffers in parenteral products (injections) are acetate, phosphate,
citrate and glutamate.
❑Prevent tissue irritation (ophthalmic formulations); The lacrimal fluid has a pH in rang 7
– 8. The buffering agents commonly used in ophthalmic preparations include borate,
carbonate and phosphates

5. BUFFER EQUATION
❑The pH of a buffer solution and the change in pH upon the
addition of an acid or base can be calculated by use of the buffer
equation.
❑This expression is developed by considering the effect of a salt on
the ionization of a weak acid when the salt and the acid have an
ion in common

6. BUFFER EQUATION (HENDERSON-HESSELBALCH EQUATION)
E.g. Sodium acetate + Acetic acid
When salt (Sodium acetate) and weak acid (Acetic acid) have common
ion (acetate), it can form buffer solution
Equation for w. acid
pH = pKa + Log [Salt]/[Acid]
Equation for w. base
pH = pKw - pKb + Log [Base]/[Salt]

7. FACTORS AFFECTING BUFFER SOLUTION
❑Addition of neutral salts…. changes pH by altering ionic strength
❑Dilution … as it changes ionic strength
❑Temperature… pH increases with increase in pH for acetate buffers

8. BUFFERS IN PHARMACEUTICAL AND BIOLOGIC SYSTEMS
Blood is maintained at a pH of about 7.4 by the so-called primary buffers
in the plasma and the secondary buffers in the erythrocytes
The plasma contains carbonic acid/bicarbonate as buffers. Plasma proteins,
which behave as acids in blood, can combine with bases and so act as
buffers.
In the erythrocytes, the two buffer systems consist of
hemoglobin/oxyhemoglobin
The dissociation exponent pK1= 6.1 for ionization of carbonic acid in the
plasma at body temperature
The buffer equation for the carbonic acid/bicarbonate buffer of the blood
is
pH = 6.1 + log
[HCO3−]
[H2CO3]

9. BUFFERS IN PHARMACEUTICAL AND BIOLOGIC SYSTEMS
Lacrimal fluid or tears have a great degree of buffer capacity, allowing
dilution of 1:15 with neutral distilled water before an alteration of pH is
noticed. This is called as dilution value instead of buffer capacity. The pH
of tears is about 7.4 with a range of 7 to 8 or slightly higher. Discomfort
to the eyes and flow of tears will occur below pH 6.6 and above pH 9.0.
Pure conjunctival fluid is more acidic than the tear fluid.
Urine : The urine of a normal adult has a pH of about 6.0 with the range
of 4.5 to 7.8. When the pH of the urine is below normal values, hydrogen
ions are excreted by the kidneys.

10. BUFFERS IN PHARMACEUTICAL AND BIOLOGIC SYSTEMS
Pharmaceutical buffers : Buffer solutions are frequently used in pharmaceutical
practice for formulation of ophthalmic solution. Many buffer systems were
suggested by different scientists, having different range of pH
Gifford suggested that the two stock solutions, one containing boric acid and the
other containing monohydrated sodium carbonate which, when mixed in various
proportions, yield buffer solutions with pH value 5 to 9.
Sorensen suggested a mixture of salts of sodium phosphate for buffer solutions of
pH 6 to 8. Sodium chloride is added to each buffer mixture to make it isotonic
with body fluids.
Hind and Goyan suggested a buffer system containing boric acid, sodium borate
and sufficient sodium chloride to make the mixtures isotonic
Clark-Lub postulated the following buffer mixtures : (i) HCl and KCl, pH 1.2 to 2.2
(ii) HCl and potassium hydrogen phthalate, pH 2.2 to 4.0 (iii) NaOH and
potassium hydrogen phthalate, pH 4.2 to 5.8

11. PROBLEM 1
What is the pH of 0.1 M acetic acid solution, pKa =4.76? What is
the pH after enough sodium acetate has been added to make the
solution 0.1 M with respect to this salt.

12. PROBLEM 1
What is the pH of 0.1 M acetic acid solution, pKa =4.76? What is
the pH after enough sodium acetate has been added to make the
solution 0.1 M with respect to this salt.

13. PROBLEM
What is the pH of a solution containing 0.10 mole of ephedrine
and 0.01 mole of ephedrine hydrochloride per liter of solution?
The pKb of ephedrine is 4.64.

14. PROBLEM
What is the pH of a solution containing 0.10 mole of ephedrine
and 0.01 mole of ephedrine hydrochloride per liter of solution?
The pKb of ephedrine is 4.64.

15. BUFFER CAPACITY
❑The buffer capacity of a buffer solution is “a measure of its
magnitude of its resistance to change in the pH on an addition of
an acid or a base.”
❑Buffer capacity is also referred as buffer index, buffer value,
buffer efficiency or buffer coefficient.

16. BUFFER CAPACITY
The buffer capacity represented by ‘β’ may also be defined as:
❑“The ratio of the increment (amount added) of strong acid or
base to the change in pH (ΔpH) occured”.
❑β = ΔA or ΔB / ΔpH
Where, ΔA or ΔB represents the small increment (in gram
equivalents / litre of strong acid or base added)and ΔpH is the (small) pH
change of ΔpH.

17. THANK YOU