I use 1 ml of plant extract of different solvent (chloroform, hexane and methanol), and I prepare 5.9 mg of DPPH in 100 ml of methanol and check absorbance at 517nm. So please suggest how I can prepare positive control sample for ascorbic acid for above method. Even though I didn't measure the concentration of liquid extract. I want to calculate the % inhibition.
yes by plotting calibration curve with various concentrations of ascorbic acid you can calculate the ascorbic acid equivalent % inhibition of your extract.
But to know the exact amount of substance that shows % inhibition equals to any concetration of ascorbic acid, it is necessary that how much of plant material you have extracted in what volume of solvent. Because only after that you should be able to conclude that how much of plant extract equals the % inhibition of specific concentartion of ascorbic acid.
In my opinion, ascorbic acid would not be need. You can use the solvent, which solubilized your sample, as the positive control. The positive control will be done with same protocol as sample, but use the positive control instead of sample. Then, calculation %inhibition as following equation;
%inhibition = 100 x (A517 of control - A517 of sample) / A517 of control
Hopefully, my answer make you clear.
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