Rf values and Chromatography

[majinknight]

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.

 

[Mertas]

Hi,

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.

 

[wais]

Hi there,

Thank you for sharing your experience with the chromatography lab. It sounds like you have encountered some challenges with your results and understanding the Rf values. Let's discuss some possible explanations for the discrepancies you have noticed.

First, it is important to note that Rf values can vary depending on the solvent used and the conditions of the experiment. Even small differences in the composition or temperature of the solvent can affect the separation of pigments and therefore the Rf values. So, it is possible that the Rf values you calculated in your lab may not match the standard values found online due to these variations.

Another factor to consider is the accuracy of the measurements and calculations. It is possible that there were some errors in measuring the distance traveled by the pigments or in calculating the Rf values. This could explain why your results are not matching with others online.

In terms of the colors observed on the chromatography paper, it is important to remember that different pigments may appear as different shades of the same color. For example, chlorophyll b is typically described as olive green, but it can also appear as a yellow-green. This could explain the difference in the colors observed by your teacher and those found online.

In conclusion, it is important to keep in mind that there can be variations in the Rf values and colors observed in chromatography experiments. It is always a good idea to compare your results with others and discuss any discrepancies with your teacher. You can also try repeating the experiment with different solvents to see if you get similar results. I hope this helps and good luck with your future experiments!