2. INTRODUCTION
For thousands of years ago, every people have known that lemon juice, Amla, and
many other food items having sour taste. Still, only a many hundred times ago it
was proposed that those effects sour taste because they contain ‘acids’. The term
acid comes from Latin term ‘accre’ which means sour.
It was first used in the seventeenth century by Robert Boyle to label substances as
acids and bases according to the following characteristics:
The various substances were act as acid & bases as per the observed properties of
the aqueous solutions.
The above substances shows different property but when any substance not
changes the color of litmus paper and Ph also constant i.e. 07 then this substances
is called as Neutral. The different investigators characterize acids and base by
different concepts or theories as follows.
Acid Base
1. Sour Taste
2. Converts blue litmus red
3. Ph less than 7
4. are corrosive to metals
5. become less acidic on mixing with
bases
1. Bitter burning taste
2. Converts red litmus blue
3. ph above 7
4. feel slippery or soapy
5. become less basic on mixing with
acids
3. BUFFER EQUATION
BUFFER EQUATION HENDERSON'S EQUATION (pH OF A BUFFER)
The buffer equation is also known as Henderson-Hasselbalch equation.
These two equations are obtained separately for acidic and basic type of
buffer.
Buffer equation is developed which is depends on the effect of salt on the
ionization of a weak acid, when the common ion present in salt and acid.
The relationship between Ph and Pk concentration of a weak acid and
conjugate base is expressed by Handerson-H asselbalch equation.
4. Buffer capacity (β) is defined as the moles of an strong acid or strong
base required to change the pH of a solution by 1, divided by the pH
change and the volume of buffer in liters.
it is a unit less number.
Larger the buffer capacity better will be the buffer because, it can
accumulate more acid and base without significant change in pH.
β=BpH
β=buffer capacity= buffer efficiency= buffer index= buffer value.
Small increment in gram equivalents/Liter of strong(oracid) added to the
buffer soln. to produce a pH change of ΔpH.
5. BUFFERS USED IN PHARMACY
A. Standard Buffer Solutions:
Standard Buffer Solutions are solutions of standard pH. They are used for
reference purposes in pH measurements and for carrying out many
pharmacopoeial tests which require adjustments to or maintenance of a
specified pH.
Composition of Standard Buffer Solutions
1.Hydrochloric Acid Buffer: Take 50 ml of the 0.2 M potassium chloride in a
200 ml of volumetric flask, add the specified volumeof0.2 M hydrochloric
acid and then add water to make up the volume up to 1000 ml.
2.Acid Phthalate Buffer: Take 50 ml of the 0.2 M potassium hydrogen
phthalate in a 200 ml of volumetric flask, add the specified volume of 0.2
M hydrochloric acid and then add water to make up the volume up to 1000
ml.
3.Phosphate Buffer: Take 50.0 ml of 0.2 M potassium dihydrogen phosphate
in a 200 ml of volumetric flask, add thespecified volume of 0.2 M sodium
hydroxide and then add water to make up the volume up to 1000 ml.
6. BUFFERED ISOTONIC SOLUTIONS-
The Isotonic buffered solution is defined as a solution which maintains the
iso-tonicity and the pH as that of the body fluids.
Isotonic buffer solution should be compatible with the body fluids.
There are three types of solutions in our body based on solute
concentration,
Isotonic –having concentration of solutes same in both inside and outside
of cell.
Hypertonic – the concentration of solutes is more outside of the cell than
the inside.
Hypotonic - the concentration of solutes is more inside of the cell than the
outside
MEASUREMENT OF TONICITY:
Tonicity is a property of a solution in reference to a particular membrane,
and is equal to the sum of the concentrations of the solutes which have the
capacity to exert an osmotic force across the membrane.
Tonicity may affect on solute permeability. Measurement of tonicity carried
out by using following two methods.
7. 1.Hemolytic method:
Is tonicity value can be calculated by using the hemolytic method in
which the effect of various solutions of drug is observed on the appearance
of red blood cells suspended in solution?
Red blood cells (RBC’S) are suspended in various drug solutions and the
swelling of RBC’S is observed bursting, shrinking and wrinking of the blood
cells.
In case of hypotonic solution oxyhaemoglobin is released in direct
proportion to the number of cells haemolysed.
In case of hypertonic solutions, the cells shrink and become wrinkled.
In case of isotonic solutions, the cells do not change their morphology. This
method used for the determination of isotonicity value.
8. 2.Cryoscopy method or depression of freezing point:
In this method, the quantity of each substance required for an isotonic
solution can be calculated from the freezing point depression values.
The freezing point of water is 0oC.
When substances such as sodium chloride is added to water, freezing point
of water decreases.
The depression of the freezing point (ΔTf) of blood and tears is -0.52oC.
3. Calculating Tonicity Using Liso Values
Because the freezing point depressions for solutions of electrolytes of both
the weak and strong types are always greater than those calculated from
the equation
ΔTf= Lfc,
The L value can be obtained from the freezing point lowering of solutions
of representative compounds of a given ionic type at a concentration c that
is isotonic with body fluids.
This specific value of L is written as Liso.
The Liso value for a 0.90% (0.154 M) solution of sodium chloride, which has
a freezing point depression of 0.52°C and is thus isotonic with body fluids,
is 3.4: From
