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Rf values and Chromatography

  1. Oct 25, 2004 #1
    Hi for biology we had to do a lab which we separated the plant pigments by chromatography of spinach. We used a solvent of 90% petroleum ether:10% acetone. After we did the experiment we ran out of time in class so the teacher went and recorded everyones results on there paper. The problem with this is we we got it back it was very faded, and only knew the general colour by what he circled, yellow or green. Then we had to calculate our Rf values. Now we are to compare them to the standard Rf values. I have not found all of these Rf values so if anyone knows what the standard Rf values are it would be much appreciated. Also on our chromatography paper the results of our Rf values are not very close to others on the internet. Also the colours that the teacher said appeared on the papers are not the same. Going from the solvent front to the origin the colours idicated are : yellow, yellow, yellow, green, yellow. I think the order of pigments is beta-carotene, lutein?, xanthophyll, chlorophyll a, and chlorophy b. But chlorophyll b is suppose to be olive green and what was idicated on our paper was yellow. The rest appear to seem right, order was but the Rf values seem to high for some. Any help would be much appreciated.
  2. jcsd
  3. Oct 28, 2004 #2

    If I were you, I would follow the way like this: First of all, you should be sure that you do the standart experiment for the Rf values. If the data you found in the net don't correspond with the experiment you do, or you don't do the standart method for this, then it is not a good referance.

    If you cannot find a standard, then you will do an experiment first and compare the other experiments with respect to the results of this first experiment which will be regarded as standart. The solvent system is fixed, no problem. The sample is fixed too, again no problem. So the place of the spots will be same too. You will calculate the Rf values and determine the color of spots; and take these as standarts. Then you will perform your experiments and compare your results with this standart ones you calculated (But here, you should have info on the nature of the spots - which one comes first and color etc.). I think this way would be easier to evaluate, at least you will find similar results.
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