MadSci Network: Chemistry

Re: Where can I find tables of Rf values?

Date: Mon Jul 10 17:09:29 2000
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Chemistry
ID: 963260691.Ch

There is no such thing as a table of Rf values. Chromatographic retention times are sensitively and unpredictably dependent on the conditions; if you run chromatography on the same sample three consecutive times (using the "same conditions") you will get different retention values (Rf or whatever) for the same substance each time!

That's not to say that the values will be wildly different; in sensitive techniques such as gas chromatography you get almost the same values for the same substance on consecutive runs. But with TLC the only way to unambiguously identify something is to run an authentic sample on the same plate as the substance to be identified. Not "another plate, right afterwards." The same plate.

That's why you will never find a table of Rf values. Or of GC retention times, for that matter.

Dan Berger
Bluffton College

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