Sources of impurities in medicinal agents

1. By
Mrs. Shinde Pooja N.
SPMS College of pharmacy, Akluj.

2. Impurity is the undesirable foreign material or unwanted material
present in pharmaceutical substances which may or may not be
toxic.
Sources of impurities
1. Raw material -
Raw material should be of pure quality.
If impurties are present in raw material then these may carried in final
product
Example – Copper sulphate is prepared by addition of sulphuric acid
in copper. If copper contains impurity beyond the limit the final
product also contains impurity beyond the limit.
Cu + H2SO4 CuSO4 + H2

3. Reagents used in manufacturing process should be completely
remove impurity by washing with water or any other appropriate
solvent
.
Example - Precipitate of calcium carbonate prepared by using
calcium chloride and sodium carbonate. When these react with each
other it form precipitate of calcium carbonate. If this precipitate is
not properly washed with water it may contains carbonate as an
impurity.
CaCl2 + NaCO3 CaCO3 + 2NaCl2

4. Sometimes some intermediates are formed during manufacturing
process which will converted into final product.
Example – Potassium iodide is prepared by reaction of potassium
hydroxide and iodine. Potassium iodate is intermediate product
which is converted into potassium iodide when it heated and
prepared with charcoal.
If potassium iodate is not properly heated and evaporated with
charcoal it will not get completely converted into potassium iodate.
Potassium Hydroxide + Iodine Potassium iodate
Potassium iodide

5. To prepare any substance or any chemical compound it require
proper mixing, suitable temperature and PH.
If mixing is incomplete at unsuitable temperature and PH then it
contains impurity in final product.
Example - Emulsification

6. Water is one of cheapest solvent which is commonly used.
There are many types of water
1. Tap water
2. Soft water
3. Demineralised water
4. Distilled water
1. Tap water – It contains calcium, magnesium, sodium
chloride as an impurity therefore not used in manufacturing.
It used for washing apparatus.
2. Soft water - Prepared by passing tap water through sodium
zeolite candle where divalent ions are replaced with
sodium. It means it contains more amount of sodium
impurities, so it not used for manufacturing.

7. 3.Demineralised water –
Minerals are absent.
It is better solvent but it contains organic impurities.
4. Distilled water –
Prepared by distillation.
It is free from organic as well as inorganic type of impurities.
So it is ideal solvent used in manufacturing process.

8. Most commonly used metal are stainless steel, aluminium,
copper, iron and glass are also used for construction of vessel.
Some reagents used in manufacturing process react with metal
and traces of metal incorporate in to solution and finally
contaminate the product.
Similarly glass vessel may traces alkali to the solvent.
Example – Strong acid leaches out alkali from borosilicate
glass.
Copper and zinc react with slightly acidic substances.
Stainless steel and hard glass commonly used for
manufacturing of vessels. It contains less amount of impurities.

9. Some pharmaceutical chemicals undergoing chemical
decomposition if they are not stored properly.
Example – 1. Ferrous sulphate
When exposed to air it becomes brownish.
2. Some drugs get decomposed due to light so it should be stored
in light resistant container. Example amber coloured glass.

10. Some pharmaceutical chemicals may adulterated with cheaper
substances.
It have some physical properties.
Example – Potassium bromide may adulterated with sodium
bromide. Both have same physical properties.
Sodium bromide is cheaper substance