Does anyone know how to analyse antioxidants?

Question

I need to find out how to analyse different antioxidants and find out which one is more effective, any ideas?

Answer 1

In terms of sheer ability to reduce oxygen, you could carry out a titration.  Adding a controlled amount of oxygen gas is very difficult, so it would be much easier to titrate with another oxidizer such as hydrogen peroxide (peroxide, superoxide, and other such oxidizing species are more commonly removed by antioxidants in the body than is molecular oxygen).

You will need a redox indicator for the titration.  Iodine is one such indicator, especially when starch is added to form a dark complex.  Oxidizers will oxidize iodides to iodine, triggering a color change in the solution.  The only potential problem here is that the antioxidant you are trying to study might be a worse reducing agent than iodide, so you might end up oxidizing the iodide before your compound.

If this is the case, you can try another indicator - diamminecopper(I) salts or reduced methylene blue might both work (both becoming blue on oxidation).

Anyway, if you decide to use iodide, add potassium or sodium iodide to the antioxidant solution, along with a small amount of starch.  Stopper a vial of a known volume of this liquid (to prevent more oxygen from getting in).

To reduce hydrogen peroxide, the solution will need to be acidified - 2 molar equivalents of a strong acid should be added to the hydrogen peroxide solution (will form only water as reduction product) - be careful with HCl as it often contains free Cl2 that will oxidize the iodide and/or antioxidant.  You will probably need to standardize this solution: a different procedure is used depending upon the concentration that you use.  Fill this solution into a buret.

Add a stir bar to the flask and place on a magnetic stirrer.  Fit the buret to the flask through a rubber stopper with a hole, or in some other fashion such that no air can be admitted to the reaction flask.  Slowly add hydrogen peroxide until the dark color of iodine is observed (and doesn't go away in a few seconds), and record the volume of peroxide solution dispensed (if it observed immediately, you will need a different indicator for this antioxidant).  By comparing this amount, you can compare the activities of various antioxidants.  Bear in mind that this does not necessarily correlate to their actual performance inside living organisms.