Dear Subha Dharmalingam,

You can  build a Scatter Plot of % oxidation inhibition vs. concentration (ug / ml), and  add the best regression line fits the data by following steps: (1) select one of the points on the graph, (2) click on the right mouse button and from the menu select "Add Trend line", (3) select the type of regression  tick both "Show graph's equation " and "Display R-squared value" , the more closer R2 to 1.00, the better is the fit and (4) use the Regression Equation to Calculate IC50.

for more details see the following link:

http://www.ncsu.edu/labwrite/res/gt/gt-reg-home.html

Alternatively you can do the same job manually taking into consideration

% inhibition = [Absorbance of control - Absorbance of test sample/Absorbance of control] X 100

The effective concentration of sample required to inhibit by 50% (IC50 value) can be obtained by linear regression analysis of dose-response curve of %inhibition vs. concentrations.

Please note if you monitor a decrease in the absorbance of an oxidant that is being inhibited  you should get an equation of the type Y= mx + C.

Hoping this will be helpful,

Rafik

 Dear Rafik Karaman,

Thank you very much,your answer is very  helpful to me

Dear Subha,

If you have Graphpad prism software, then it is easy to obtain actual value of IC50. Just move the cursor on the graph till you get the Y coordinate 50. Corresponding X coordinate is the IC50 value.

Dear Pradeepa V Samaga,

Thank you so much for your information. I have downloaded the graphpad prism software and I tried to calculate IC50 using this software.But I am unable to find out the same.If you can please explain briefly.

Sincere thanks,

D.Subha

The extract concentration providing 50% of inhibition (IC50) is calculated from the graph of inhibition percentage.

please find enclosed an article that explains the method of calculation of IC50.

bests regards

Dear Yassine ez zoubi,

Thank you so much 

Thanks.