Recently I had a sample with a huge antioxidant capacity, so I had to dilute it. Do I have to change anything in my scavenging calculations for the right IC 50?
Hi Peter E.
first dilute your sample in microgram (5,10,15,..n) than find the %inhibition from
( cnt od- sample od)/(cnt od) *100 this equation and put these value in linear graph calculate the IC50 value from (y=mx+c) equation.
Dear Peter E.,
It seems like you are asking if dilution of the sample affect the IC50 calculation.
First of all, if your sample is solid (like dried plant extracts), you would have it's concentration expressed in units of mass per volume such as mg/mL. It's concentration changes on dilution and you have less mass per volume of the solvent. So, you have solutions of the sample with different concentration. Eg. 5, 10, 20, 40, 60 ppm. After it's reaction with DPPH of a known concentration, for e.g., 40 ppm you will have absobance drop which is proportional to the amount of antioxiant in the sample. You may have DPPH calibration curve prepared before to measure the exact amount of DPPH before and after reaction with the sample. You may also express it in percent as mentioned by Mr. Negi. Since you must use linear or nonlinear methods for calculation of IC50, which is the concentration of your sample that scavenged 50% of the DPPH, you must know the concentration of your sample.
You don't have to do any changes in calculating IC50 of extract. Simply dilute your extract using appropriate solvent such as ug/ml or mg/ml depending on activity you have observed and calculate the inhibition of DPPH radical in percentage then plot a correlation graph between concentration (as you have diluted the extract) and percent inhibition and get the value of equation y=mx+c and calculate IC50 value. Less the IC50 value indicates higher antioxidant potential of extract.
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