I am working on crude oil and want to conduct SARA analysis which involves sequential elution with multiple solvent systems (4 as per ASTM procedure) i wany to know how to change solvent system in singlw column? And also if possible please explain how the same is done in thin layer chromatography.
In column LC you add different eluent at the top. In HPLC if you have a gradient pump you can make a program/change a channel. For TLC the cage with rods is placed in special oven and after that placed in a chamber with different eluent
Regards
G
Dear Sir. Concerning your issue about the detailed process for column chromatography with multiple solvent systems. Solvent systems for use as mobile phases in column chromatography can be determined from previous TLC experiments, the literature, or experimentally. Normally, a separation will begin by using nonpolar or low polarity solvent, allowing the compounds to adsorb to the stationary phase, then SLOWLY switching the polarity of the solvent to desorb the compounds and allow them to travel with the mobile phase. The polarity of the solvents should be changed gradually. On a macroscale, the mixing of two solvents can create heat and crack the column leading to a poor separation. Some typical solvent combinations are ligroin-dichloromethane, hexane-ethyl acetate and hexane-toluene. Often an experimentally determined ratio of these solvents can sufficiently separate most compounds. Solvents such as methanol and water are normally not used because they can destroy the integrity of the stationary phase by dissolving some of the silica gel. I think the following below links may help you in your analysis:
http://courses.chem.psu.edu/chem36/Experiments/PDF's_for_techniques/CC.pdf
https://indigo.uic.edu/bitstream/handle/10027/21034/Solvent%20System%20Selection.pdf?sequence=2
http://www.scielo.br/pdf/qn/v36n6/17.pdf
Thanks
Hi Payas,
It is pretty easy to change solvents during column chromatography. You just have to take care of timings. So if you have four solvents namely A.B.C.D. When your column is running with solvent A, and you want to change it to solvent B, then wait until solvent A reaches to the silica bed. As soon as it reaches almost 5 mm below your silica bed in column, immediately add solvent B using very fine dropper via sides of column slowly so that the silica bed is not disturbed and keep on adding until you add atleast 5 cm of solvent B above silica bed. Then let that reach silica bed and again add solvent B upto 5 cm followed by more addition via funnel. Repeat this procedure for all the four solvents you want.
Good Luck
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