Tonicity, Isotonic solutions, Hypotonic solutions, Hypertonic solutions, Interface, Surface, Absorption, Adsorption, Surface tension, Solubilization, Polymorphism

Tonicity:

Tonicity is measure of the osmotic pressure of two solutions separated by a semi permeable membrane.

Isotonic solutions:

Two solutions are said to be iso-osmotic or isotonic if they exert the same osmotic pressure when separated by a semi permeable membrane.

Example: 0.9 % solutions of NaCl is said to be isotonic solutions.

Hypotonic solutions:

Solutions with osmotic pressure lower than that of the body fluids or of 0.9% NaCl solution are called hypotonic solution.

Hypertonic solutions:

Those solutions having a higher osmotic pressure than the body fluids or of 0.9% NaCl solutions are called hypertonic solution.

Interface:

The boundary between two phases is generally described as an interface.

Surface:

When one of the phases is a gas or a vapor and the other a liquid or solid, the outer space of the phases which is contacted or exposed with the outer space of other phases is called surface of that phase.

Absorption:

Absorption is the incorporation of a substance in one state into another of a different state.

Adsorption:

Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solid particles to a surface.

Surface tension:

Surface tension is a property of the surface of a liquid that allows it to resist an external force.

Solubilization:

The process by which water insoluble or partly soluble substances are brought into aqueous solution by incorporation into micelles is termed as solubilization.

Polymorphism:

Polymorphism is the ability of a compound(or element) to crystallize as more than one distinct crystalline species with different internal lattices.

or

Polymorphism (or crystal polymorphism) is a phenomenon related to the solid state; it is the ability of a compound in the solid state to exist in different crystalline forms having the same chemical composition. Substances that exist in a non-crystalline solid state are said to be amorphous.

Rate of reaction, Zero Order Reaction, First order reaction, Second order reaction

Rate of reaction:

The rate of a chemical reaction is defined as the velocity with which a reactant or reactants undergo chemical change.

Zero Order Reaction:

If the rate of a reaction is independent of the concentration of the reacting species, the reaction is said to be a zero-order reaction.

First order reaction:

A first order reaction is one where the rate depends on the concentration  of the species to the first power.

Second order reaction:

A second order reaction is one where the rate depends on the concentration of the species to the second power.

Buffer solutions, Buffer action, Buffer capacity, Factors affecting pH of Buffer Solutions, Biological buffers, Pharmaceutical Buffers

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.