Questions about chromatography with flower pigments

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Questions about chromatography with flower pigments

Postby Elizabeth00 » Sat Jan 19, 2013 5:46 pm

I have finished performing the experiment for "Reveal the Red: Chemistry of Flower Pigments". I have some questions about interpreting some of my results. I used 35%, 50%, and 70% isopropyl alcohol as solvents, and I tested 6 different red flowers. Some of the flowers separated into two pigment bands (Rf .80, .95) which were the same color (a purplish-red). These two pigment bands have the same color, but different Rf value....are they two different pigments? Also, what exact information can I get from the Rf values....does it just show that there are different pigments present, or can I use Rf value to identify what the exact pigment is. It is confusing because I've read that you can use Rf value to identify the pigment, but that the Rf value is different for different solvents. Is there a Rf reference guide for 50% isopropyl alcohol?
Elizabeth00
 
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Joined: Fri Jan 11, 2013 10:47 am
Occupation: Student
Project Question: Revealing the Red: Exploring the Chemistry of Red Flower Pigments
Project Due Date: Feb. 10, 2013
Project Status: I am conducting my experiment

Re: Questions about chromatography with flower pigments

Postby donnahardy2 » Mon Jan 21, 2013 9:07 am

Hi Elizabeth00,

It sounds like you are doing this excellent project from the Science Buddies website:

http://www.sciencebuddies.org/science-f ... p035.shtml

If you have two red bands with different Rf values, these are definitely different molecules.

I have not been able to find a reference that includes Rf values of red plant pigments in isopropanol, although I'm sure that this information must exist. Why don't you go to Google Scholar and search for the specific information on red flower pigments.

What flowers did you use for your experiment?

Donna Hardy
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Re: Questions about chromatography with flower pigments

Postby donnahardy2 » Tue Jan 22, 2013 5:59 pm

HI Elizabeth00,

Here is some additional information about the identification of flower pigments. Your question about the identification of the specific pigments is a good one, however, I have not been able to find any published data on Rf values of red plant pigments in isopropyl alcohol. Anthocyanins are not particularly stable, so I don't think you would be able to obtain known standards to run to verify the identify.

My only suggestion is to do a search for the specific flowers you have tested and find out if anyone has published the identify of the anthocyanin pigments in the literature. If you can find the name of the specific anthocyanins, you can probably confirm that the bands contain those pigments. Otherwise, you will have to conclude that identifying the pigments is beyond the scope of your current project; However, you could impress the science fair judges by explaining what you would do in order to complete the identification.

Here are two references on red plant pigments. These are good references because you can access the full text and read all of the details. Please note the techniques used to identify the pigments require specialized equipment. The first article reports the structure of a red plant pigment found in red carnations. The second article is good because it includes a color photograph and the structure and name of the red plant pigments in red carnations and red cyclamens.


http://pubs.acs.org/doi/pdf/10.1021/jf9907642

http://www.wdc-jp.biz/pdf_store/jspcmb/ ... 29_215.pdf

You can go to Google Scholar and search for "anthocyanins in the name of the flower you tested." Be sure to use the name of the genus you studied instead of the common name.

For the analysis of your results, you can say the the flowers that showed two bands have at least two pigments and that the two separate bands are different pigments. However the bands that have identical Rf vales could be the same pigment, but may be different pigments.

I hope this helps.


Donna Hardy
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Re: Questions about chromatography with flower pigments

Postby Elizabeth00 » Tue Jan 29, 2013 4:57 pm

Thanks for the information!
Here are the flowers that I used: Tulips, Roses, Hibiscus, Geraniums, Bougainvillea, and Carnations.
Elizabeth00
 
Posts: 2
Joined: Fri Jan 11, 2013 10:47 am
Occupation: Student
Project Question: Revealing the Red: Exploring the Chemistry of Red Flower Pigments
Project Due Date: Feb. 10, 2013
Project Status: I am conducting my experiment


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