I used different concentrations of a sample, and at a lower concentration i obtained negative percentage of DPPH inhibition, why the negative value please, thanks.
If your control value is less than your sample value, you can get a negative value. As DPPH value represented in percentage negative value is not correct, probably your sample concentration is very high. In that case you can serially dilute your sample and perform the test again. Find out in what dilution factor gives positive result.
To handle this problem you have to calibrate the analysis with solvent blank, sample blank and control.
Because of the high concentrations of the extract or the effect of the color of the extract Ya'U Sabo Ajingi Muhammad Muneeb Ahmad Houari Fatima Zohra Nabanita Ghosh
You need to check the colour interference between your sample and control at 517nm
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