Chromatograms

[orbit]

Hi all, does anybody know if there is a good site on the internet that can provide me with information regarding the analysis of paper chromatograms? I have taken some samples during a lab class and now have to do a small assignment based on them. I’m not really sure on how to analyze them properly. Any help would be greatly appreciated 🙂

[blcr11]

http://inst.sfcc.edu/chemscape/catofp/c … m#identify

http://images.apple.com/education/curri … tology.pdf

For two. Basically you need to measure the Rf (relative mobility) of samples with respect to the solvent front and compare the Rf of known samples with those of an unknown. The color of the spot or its reactivity toward various detection reagents can also help identify an unknown.

There are several tomes available on chromatography in general which will include paper methods, but I suspect these will be more than you want to read and you’ll have to go back to things published prior to the 1980s probably if you want much of a discussion about paper chromatography. Thin layer chromatgraphy is still used as a preparative technique in organic labs, as well as hplc, gc/ms or lc/ms, but paper is rarely used anymore.

[orbit]

Thanks for your help but I’m still a bit confused. All we have a 4 different plant samples. All we did was put the plant pigment on the paper and the tutes did the processing of them. We have not been given anything to reference them against. We can see the chlorophyll and carotene etc but they are all spread out to different degrees. Does this mean that the pigments that have spread further are the ones the plant has more of? Or just that the molecules are faster moving or something? Thanks again, any help would be greatly appreciated 🙂

[blcr11]

That’s the problem with paper chromatograms, the spots are often more like smears than spots. Spotting technique has something to say about how much the spot spread at the origin; the sharper the application spot, in general, the sharper will be the final spot. Substances that move the fastest are also likely to be the most smeared.

How a substance moves on the chromatogram has little to do with how much of it there is in the sample. Instead, its a matter of its relative affinity for the stationary phase (paper) and the mobile phase (the solvent system). The cellulose of paper is polar due to the sugar hydroxy groups while the solvent system (I’m guessing) was a mixture of organics (butanol/chloroform maybe or something like that). You spot a sample on the paper and let the solvent move up the chromatogram by capillary action. As solvent moves over the sample, those things that are most soluble in the mobile phase dissolve in and are carried along with the solvent while the more polar substances are still held in place by the non-moving paper. The more polar compounds do dissolve in the mobile phase, but move more slowly on the chromatogram because the stationary phase is always attracting it, slowing it down at each "step." Now, the same thing is happening to the more rapidly moving material, but its affinity for paper is not so great, so the stationary phase offers much less resistence to moving compared to a more polar substance. What you end up with is a range of mobilities from least to most polar as you go from fastest to slowest moving spots, with "fastest" meaning closest to the solvent front and "slowest" meaning nearest the application point.

[orbit]

Thank you all very much for your help 🙂

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