Chromatography, Chemistry

The process of chromatography involves passing a mixture dissolved in the "mobile phase" through a stationary phase, which separates the analyte which is to be measured from the other molecules in the mixture based on differential partitioning in between the mobile and stationary phases. Subtle differences in a compound's partition coefficient resulting in differential retention on stationary phase and therefore changing the separation. Method of chromatography is stated below.

Paper chromatography is a technique which involves placing a small dot or line of sample solution onto the strip of chromatography paper. The paper of it is made of cellulose, a polar substance, and compounds within the mixture travel farther if they are non-polar. More polar substances bond with cellulose paper more quickly, and thus do not travel as far. The paper is placed in a jar having a shallow layer of solvent and sealed. As the solvent rises through the paper, it meets sample mixture which begins to travel up the paper with the solvent. 

Thin layer chromatography (TLC) is an extensively employed laboratory technique and is similar to paper chromatography. But, instead of using the stationary phase of paper, it involves a stationary phase of the thin layer of adsorbent such as alumina, silica gel, or cellulose on a flat, inert substrate. Compared to paper, this has the advantage of faster runs, better separations, and the choice among different adsorbents. For even better resolution and to allow for the quantification, high-performance TLC can be used.

Column chromatography is the separation technique in which the stationary bed is within a tube. The particles of the solid stationary phase or the support coated with a liquid stationary phase may fill the whole inside volume of the tube (packed column) or be concentrated on or along the inside tube wall leaving an open, unrestricted path for the mobile phase in the middle part of the tube (open tubular column). Differences in rates of movement through the medium are calculated to different retention times of the sample. 

Posted Date: 9/14/2012 9:27:31 AM | Location : United States

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