[Akira]

Hi, I'm new. I'm a highschool student, and I am in great need of help with my chemistry project. I had to pick a topic and write up an experiment for it. (but not actually carrying out the experiment)

My topic is on tea. I plan on researching for which kind of tea contains the highest amount of polyphenols. The teas I plan on using are Green, Black, White, and Oolong.

I'm having alot of trouble getting a start on this because at the same time, my teacher is teaching us about chemistry as we progress with our research. So I'm wondering what kind of analytical methods there are to finding out polyphenol content in tea. One person (not on this forum) suggested I see at what wavelength polyphenols absorb ultraviolet radiation, and measure that. The person also mentioned that the concentration was proportional to the absorbance according to Beer's Law.

I'm not sure how effective that method would be, so I'm hoping there would be a somewhat easier method. I also have trouble understanding Beer's law.

Thanks agian for the help, should someone provide me with any. Other information on polyphenols would also be greatly appreciated!

[Akira]

The informal chemical education community is quite small, so if you tell us who has already helped you, we probably know who they are.

If you were interested in a particular compound, lets say the amount of caffeine in tea. Then it would be a simple procedure to run your sample though an Liquid Chromatography apparatus and quantitate the amount of caffeine in each differeing tea. When your interested in a class of molecules like polyphenols it becomes more problematic.

Well the person that made the suggestion to me was on a livejournal community, and posted anonymously.

As for the polyphenols part:

Oh ok, so polyphenols isn't a good idea to quantitate the amount for? In that case, would moving to catechins be better? Because, correct me if I'm wrong, I believe that catechins was a chemical found in polyphenols.

(thanks for clearing up polyphenols for me by the way)

[hemispheredancer]

Catechins all fall into the subclass of polyphenols.   Due to the fact that there are so many polyphenols present in teas, you do have a problem quantifying them all.  
The problem with using UV detection to quantify the polyphenols is that they all have different Exctinction Coefficients.  Beers Law states that E=Abc or that the Extinction Coefficient is equal to the absorbance x path lenght of the detector cell x concentration.  Solving for the concentration you would need to know all other variables.  
I think that you may be able to identify and quantify the catechins in teas a little easier.  Because there are only 5 different catechins that need to be identified its and easier process.  Do you need to have access to the equipment even though you're not actually running the experiment?  That would make a big difference in how to proceed.

Take a look at this page.  http://web.uccs.edu/lasdean/hompesch.pdf
I know that some of the science would be difficult to understand at a high school level but it might lead you in the right direction.  Let me know and Id be happy to help more.

[Akira]

cool. Thanks for the link! That helped alot.

[corey2]

The final solution should be using a HPLC-MS spectrometer, for separation and identification.

For Akira (highschool level)
HPLC-MS= High pressure liquid chromatograph with a mass spectrometer as detector.