Rf values help?
Rf = (dist. moved by solute)/(dist moved by solvent).
How do you know how to identify the components of mixtures by means of their Rf values?
please drop down some answres
thx for read ing and answering my qustiion thank you once again
Rf values pertain to certain components of a mixture that you want to separate by
chromatography. Let's say you put a drop of a mixture A onto a paper chromatography sheet and
dip it into the separating mixture. As the mixture moves up the paper, different components of A
have different affinities to the paper and the solution. Lets say component 1 has more affinity to
the paper than component 2. Therefore Component 2 is going to move further up the paper in the
same space of time as componenet 1. Let's say that component 1 moves a distance "C1" and
component 2 moves a distance "C2". The separating mixture moves a distance S which is
(obviously) greater than both C1 and C2 because it's going to move those components. The Rf
value for component 1 is C1/S and the Rf for component 2 is C2/S. These values are constant for
each component in a given separating mixture, pressure, T and chromatography paper type and
are given in literature. By comparing the Rf values that you get for unknown components you
have and the Rf values in literature (under the same conditions), you can find what your
unknown components are.
http://answers.yahoo.com/question/index?qid=20070922133354AANUoRB
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
Message:
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
cs.bluffton.edu/~berger
http://www.madsci.org/posts/archives/2000-07/963425409.Ch.r.html
Christina03-23-2006, 04:40 PM
Would anyone happen to know where I could find the standard Rf values (for
Chlorophyll a, Chlorophyll b, Xanthophyll, and Carotene) if varsol is the solvent? I'm
trying to identify those plant pigments via Paper Chromatography, and I'd like to
compare my results to the standards. The problem is, I've been looking and can't find
it.
ankankakka
03-30-2007, 07:21 AM
This is what you can use:
"Rf values will be unique for each solvent. However, the general order of the Rf values
should be the same because the more nonpolar pigments move farther in nonpolar
organic solvents.
A recent plant physiology manual (Reiss 1994) identifies six pigments from spinach
leaves extracted with hexane and chromatographed with petroleum ether-acetonechloroform (3:1:1) on silica-gl chromatography. The pigments and their Rf's were:
carotene - 0.98
chlorophyll a - 0.59
chlorophyll b - 0.42
pheophytin - 0.81
xanthophyll 1 - 0.28
xanthophyll 2 - 0.15
The color of the bands can be a general guide to identify the pigments. Carotene is
orange. Chorophylls are green. Chlorophyll a is a blue-green. Chlorophyll b is a yellowgreen. Xanthophylls are yellow. Phaeophytin is chlorophyll lacking the central
magnesium ion. Pheophytin is an olive-green."
Source: http://madsci.org/posts/archives/2001-12/1008377272.Bt.r.html
(Original source cited: Reiss, Carol 1994. Experiments in Plant Physiology. Englewood
Cliffs, NJ: Prentice Hall.)
http://physicsforums.com/archive/index.php/t-115321.html