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Chromatographic Techniques Presentation Transcript:
1.Chromatographic Techniques
2.Paper Chromatography
3.Paper chromatography is a technique that involves placing a small dot of sample solution onto a strip of chromatography paper.
The compounds within the mixture travel are non-polar.
Adsorbent: More polar substances bond with the cellulose paper more quickly.
4.Paper Chromatography
5.Paper Chromatography-Procedure
The paper is placed in a jar containing a solvent such as ethanol or water then sealed.
A small concentrated spot of solution that contains the sample of the solute is applied to a strip of chromatography paper about 2 cm away from the base of the plate
6.4. As the solvent rises through the paper, it meets the sample mixture which starts to travel up the paper with the solvent.
5. Paper chromatography takes from several minutes to several hours.
7.Different compounds in the sample mixture travel at different rates due to
differences in solubility in the solvent
differences in their attraction to the fibers in the paper.
8.In this method, the solvent moves upward against gravitational force.
The only force that cause the motion is capillary force. So the speed of the process is slow.
9.In this method, the solvent is kept in a trough at the top of the chamber and is allowed to flow down the paper.
The liquid moves down by capillary action as well as by the gravitational force.
In this case, the flow is more rapid as compared to the ascending method.
10.Because of this rapid speed, the chromatography is completed in a comparatively shorter time.
The developing solvent is placed in a trough at the top which is usually made up of an inert material.
The paper is then suspended in the solvent. Substances that cannot be separated by ascending method, can be separated by the above descending method.
11. After development, the spots corresponding to different compounds may be located by:
their color,
ultraviolet light,
ninhydrin
or by treatment with iodine vapors.
The paper remaining after the experiment is known as the Chromatogram.
12.If Rƒ value of a solution is zero, the solute remains in the stationary phase and thus it is immobile.
If Rƒ value = 1 then the solute has no affinity for the stationary phase and travels with the solvent front.
13. The final chromatogram can be compared with other known mixture chromatograms to identify sample mixes, using the Rf value in an experiment.
14.Thin layer chromatography (TLC)
TLC is widely used.
Stationary phase solid+ adsorbent
Adsorbent like silica gel (polar), alumina.
Traveling of solvent and elute via capillary action
15.Plate preparation
TLC plates are made by mixing the adsorbent + small amount of inert binder calcium sulfate (gypsum) + water.
This mixture is spread as a thick slurry on an unreactive carrier sheet, usually glass, thick aluminum foil, or plastic (support)
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