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What do you know about the term chromatography?


Sketch a use full and detailed informative introduction on the term chromatography?
Introduction:
The purpose for the separation applicable to chemical systems is to branch or divide a heterogeneous or homogenous mixture or mass into its individual units ,components or even into elements. There are several processes and techniques for performing separation dealings which are based on some essential chemical and physical principles. 


Many of the separation procedure are very complex in nature  while others are relatively very simple and need little outlay in money, attention and effort.
The region of separation has experienced a fast growth in recent years. During this period not only have fundamental principles has been comprehensive and more clearly defined ,but newer techniques have been developed . So a lot of   available mixture which were difficult and impossible  for the purpose of  separation in the past can be separated  in recent ,some are applicable in a routine manner.  Examples of theses are to separate the following compounds:
*       Separations of amino acids
*       Rare earth separations
*       Isolation of 10 to 40 atoms of newly transuranium elements
*       Isotopes
*       Homologous series of organic molecules
*       Minerals from water
A separation  is said to be a form  of sample pretreatment where those components of the sample which will interfere the goal of separation, are removed. On the other hand if each component of the sample is to be determined, separation is performed such that each component is isolated. Consequently a method of analysis can be chosen which is based on the amount of components present rather than one kind of interferences present.the net result is that the separation methods provides additional selectivity for the ordinary instrumental and chemical methods.
A useful separative technique can be used for purification ,qualitative identification or quantitative determination. There are many different separations  whether they are mechanical  or physical


Classification of separation methods:


Several different methods have been applied to classify the separation techniques.  They may have division according to whether they involve batch discrete equilibrium steps. Or continuous none equilibrium steps, type of force involved whether they are mechanical, chemical or physical in nature. And the type of heterogonous  equillibria involved  .all of these suffer from one kind of limitation or another  because of the widely diverse properties on which separations are based it is not assemble all the separations in to one classification scheme.
Methods of separation
Methods
Basis
Precipitation
Difference in solubility
Distillation
Difference in volatility
Sublimation
Difference in vapor pressure
Extraction
Difference in solubility between two phases
Crystallization
Property of solubility at low temperature
Flotation
Difference in density between substance and liquid
Dialysis
Osmosis; flow a system through a membrane
Zone refining
Crystallization usually at elevated temperature
Electrodepsition
Electrolysis at inert electrodes
Chromatographic methods 





Adsorption column chromatography
Distribution of a solute between a solid and a liquid phase on a column
Partition column chromatography
Distribution of a solute between two liquids on a column
Thin-layer chromatography
Adsorption or partition on a open thin sheet
Paper chromatography
Partition on paper sheet
High-pressure liquid chromatography
Column liquid chromatography under high inlet pressure
Ion-exchange chromatography
Exchange of ions
Molecular sieves
Size of the solute
Gel permeation
Size of the solute
Gas chromatography
Distribution of solute in gaseous form between a gaseous and a liquid or a solid phase



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