COLUMN CHROMATORGAPHY

-

 COLUMN CHROMATOGRAPHY

  • It is a technique in which the stationary phase is solid or a liquid supported by a solid.
  • When a column is used as the adsorbent it is called adsorption column chromatography.
  • When the solid column is acting only as a support to the liquid adsorbent then it is called partition column chromatography.

SEPARATION

The selection of solvent is based on the nature of the components in the mixture. Adsorption depends upon the nature of the solvent and the adsorbent. 
The rate at which the components of a mixture are separated depends upon the activity of the adsorbent and the polarity of the solvent.
If the activity of the adsorbent is very high and polarity is low, then separation is low but gives good separation.
If the activity of the adsorbent is low and the polarity of the solvent is high, then the separation is rapid but gives poor separation


PROCEDURE

  • A proper adsorbent is selected and made a slurry with a suitable liquid and placed in a suitable tube which is plugged at the bottom with glass wool.
  • The mixture which is to be separated is dissolved in a suitable solvent and introduced at the top of the column and is allowed to pass through the column, the components are adsorbed at different regions depending on their ability for adsorption.
  • The one with greater adsorption power will be adsorbed at the top and the one with lower adsorption power will be adsorbed at the bottom.
  • The different components can be collected separately by adding more solvent at the top and this process is known as elution.
  • The weakly adsorbed component will be eluted more rapidly than the other. The different fractions are collected separately.
  • The banded column of adsorbed constituents is called a chromatogram. 
  • The components which leave the column pass through a detector and recorder. The detector produces an electric signal and the recorder converts the signal to a trace on paper. The resulting plot of the signal intensity against time is called a chromatogram.

APPLICATION

  • Quantitative separation of two or more components in a mixture.
  • Purification of substances from their components.
  • The concentration of solutes from their dilute solutions.
  • Identification of technical products.
Location: United States

Comments

Post a Comment

Popular posts from this blog

GLASS ELECTRODE

-
Image
 GLASS ELECTRODE It is a secondary reference electrode that produces a constant and reproducible electrode potential. It is an ion-selective electrode used with other reference electrodes to generate a potential difference. Construction It is made up of a special glass of relatively low melting point and high electrical conductivity, in the form of a sealed glass tube filled with 0.1M HCl, a platinum wire is inserted into it, to make electrical contact. The glass electrode is represented as Pt| 0.1M HCl | Glass | H+    The H+ ion concentration inside the electrode is constant. When the electrode is immersed into a solution of unknown H+, it becomes sensitive to the outside concentration in the solution. Such a sensitivity arises because of the difference between the H+ ion concentration inside and outside.       The electrode potential of the glass rod is : EG = EG0 + 0.0591 log [ H+ ]     EG = EG0 - 0.0591 pH  The glass electrode i...
Read more

CHROMATOGRAPHY

-
Image
CHROMATOGRAPHY  It is a method used for the separation, purification, and identification of a mixture of substances. It is useful when components of a mixture have similar physical and chemical properties and hence cannot be separated by other methods. Principle: It is based on the distribution of the components in a mixture between a stationary and a mobile phase. The stationary phase may be a column of adsorbent, a paper, a thin layer of adsorbent through which the mobile phase moves on. The mobile phase may be a liquid or gas. The principle of chromatographic separation is always adsorption (absorption of a constituent on the surface of the solid stationary phase) or partition (distribution of a constituent in between two liquid stationary phases). THEORY OF CHROMATOGRAPHY The separation takes place due to the differential migration of components which depends on the relative affinity towards the stationary and mobile phases.  The component which is less strongly held by th...
Read more

THIN LAYER CHROMATOGRAPHY

-
Image
 THIN LAYER CHROMATOGRAPHY It is a chromatographic separation method used to separate mixtures, to check the purity of a mixture, and to monitor the progress of the reaction. Procedure A glass plate coated with a material of the adsorbent will constitute the stationary phase. The material is made into a slurry or a paste and the glass plate is coated with it by a thin layer applicator and dried. This glass plate with a thin layer of stationary phase is called chromatoplate. The mixture to be separated is applied to one end of the plate and it is placed in the solvent. When the solvent reaches near the top, it is removed and dried. If the components are colored the spots can be readily located. If the components are colorless the dried plate is sprayed with a suitable reagent to make the spot colored. In this way, the position of the components is located and their Rf values are determined. Rf value is the ratio of the distance traveled by a component to the distance traveled by the...
Read more