In addition to Olalere's suggestions, for DPPH, it is advisable to store in -20 degree Celsius refridgerator.
The TAC of wines is better to evaluate under physiological conditions: water, pH 7.4. TAC depends on pH. DPPH is not soluble in water, therefore DPPH assay is not suitable for evaluation of TAC of wines. Trolox itself is badly soluble in water. Therefore, I would advise to prepare the Trolox stock solutions in phosphate buffers at pH 7.4. Solutions are unstable, unless you purge them with Ar and store in a fridge at about 0 C. The protocol of TAC evaluation of wine is described in
The determination of total concentration and activity of antioxidants in foodstuffs
By: Geletii, YV; Balavoine, GGA; Efimov, ON; et al.
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Volume: 28 Issue: 6 Pages: 501-514
Hi Judit,
I do agree with the above suggestion and further you can also get more information from the link below:
Effect of ambient temperature storage on 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a free radical for the evaluation of antioxidant activity
Article in International Journal of Biological and Chemical Sciences 8(3):1262-1268 · July 2014
DOI: 10.4314/ijbcs.v8i3.39
Good Luck.
http://ajol.info/index.php/ijbcsI
Since DPPH and Trolox are not soluble in water, they and wine samples (1:20 ratio) are solved in methanol.
Trolox is soluble in water at pH> 6 in buffered solutions. The pH of the blood serum is 7.4. DPPH is not a good model of radicals formed in vivo.
DPPH or any other CRMs stock can be stored up to 1 year with suitable conditions as per ISO 17025.
If you are asking for the methanolic solution of DPPH please, it should be stored in dark bottle tightly closed and it can be used unless the color of the solution had changed
In DPPH free radical scavenging activity It is advisable to use fresh solution.
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