Natural Impurities:

The cotton fibres are having various types of impurities. Some of them are given below:

• Pectins
• Proteins
• Colouring matters
• Mineral matters

Let us discuss above impurities one by one:

1. Pectins: It is a structural heteropolysaccharide, containing in the primary walls of terrestrial plants.

Here you may corelate it to cotton. Pectins also known as pectic polysaccharides. It is derived from pectic acid. It is high molecular weight polymer and composed of Galactouronic acid. D-Galacturonic acid is sugar acid, an oxidized from D-galactose. It is the main component of pectin, in which it exists as the polymer polygalacturonic acid.

2. Proteins: It is nitrogenous organic compounds and composed of one or more long chains of amino acids. It is present in the primary wall and Lumen. Some of the amino acid used are

• Leucine
• Leucin
• Valine
• Proline
• Alanine etc

  Some time the yellowish colour of cotton are related to Proteins and colouring matters.

3. Colouring matter: The main reason of colour in cotton is due to colouring matter. These                 colouring matter are due to presence of colour pigments.
Examples are:
3,5,7,2',4' Penta hydroxy flavone and 3,5,7,8,3',4' Hexa hydroxy flavones (Gossypetine)                      

(flavus = yellow)

3,5,7,2',4' Penta hydroxy flavone :

Molecular structure of flavone

3,5,7,8,3',4' Hexa hydroxy flavones (Gossypetine):

4. Mineral Matter: The presence of mineral matter in the cotton depends upon the soil in which it is cultivated. The quantity of  mineral matter can be determined by converting cotton  fibres in to ash and then by any suitable technique like Atomic Absorption Spectrophotometeric can be used to quantify the matter.