Re: What does the abbreviation Rf mean?

Mrs. Griffin,
I've done a bit of research into the variable Rf that you mention in your 
question.  Basically, it boils down to 
this:
Rf= distance component traveled/distance solvent traveled

Distance component traveled is measured from the origin (the starting 
point) of the sample on a thin layer 
chromatography (TLC) plate or gel  to the center of the component of 
interest.  Some sort of staining is 
involved that allows you to see your components, therefore, you can see 
where to measure to from the 
origin.

Distance solvent traveled is the TOTAL distance (from origin to where the 
chromatography was stopped) 
that the solvent traveled.  The starting and stopping points are marked by 
the researcher.

The Rf becomes important because not every gel or TLC plate is run exactly 
the same time length.  That is, 
you may run a TLC for 50 minutes the first day, but only 30 minutes the 
next day.  Or the time may vary from 
one person to another.  In any case, the component's Rf will be the same 
whether it was run 50 minutes or 30 
minutes (as long as the time was enough to allow the component to 
separate).  Thus Rf is important as a 
descriptive variable for components analyzed by TLC or gels.  

There are some stipulations.  The Rf is specific for component and solvents 
combinations.  Change the 
solvent, you'll get a different Rf and can't compare it directly to an Rf 
run in a different solvent.  
Measurements of distance have to be in the same units.

Hope this helps.

My thanks to K. Plaisance, Scientist, Univ. of Minnesota for helping me 
understand the concepts.

Ted

(Any commercial reference given, whether by name, in text or by subsequent 
web link is NOT an 
endorsement of any kind by myself, my employer or the Mad Scientist 
Network)

Admin Note:
Rf is the abbreviation for Retardation factor - the factor by which
the migration of a solute is retarded (slowed down) relative to that of
the solvent.