I'm experimenting biopolymer reducing power and currently I am following the method of Oyaizu et al. 1986.
However, when doing my positive control of ascorbic acid, I get higher reducing power for lower concentrations.
The curve is similar to a titration, it has an inflexion point around 0.6% w/v ascorbic acid, but decreases with increasing concentrations.
Anyone ever got this result? I can't backtrack the problem.
Hi Bruno,
If I understood it correctly, you are seeing an inflection point around 6 mg/mL concentration. Ascorbic acid as the positive control is used normally in the microgram scale say for instance like 5 ug/mL - 1000 ug/mL scale. So the concentration range you are using is quite high.
The normal reaction occurring here is Fe3+ -----> Fe2+ (forming Prussian blue complex in potassium ferricyanide system) and;
Ascorbic acid -------> Dehydroascorbic acid
If your reaction system is saturated, the formed dehydroascobic acid may convert back to ascorbic acid reverting the direction of Fe3+/Fe2+ conversion, this might be the reason you are seeing decreased reducing power with very high concentrations of ascorbic acid. So, simply make the ascorbic acid the limiting reagent by trying a very low concentration range as mentioned above.
Secondly, check the reaction is conducted in the correct buffer with correct pH value.
Hope this helps and let me know whether you succeed! Cheers!
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