Hi Mahmoud,

Firstly, you will need to integrate the area under the curve of the fluorescence decay (AUC) and you will need to calculate the Net AUC = AUC(standard or sample) - AUC (blank). Then, you will need to plot the Net AUC versus concentration of Trolox and to find the equation by linear regression [y (Net AUC) = A. x (concentration) + B]. This form you will get to determinate your results using the linear equation.

Best regards.

Thanks Acácio for your kind, I calculate AUC of the 4 Trolox concentration and I got the equation but I want to know why in articles use different concentration form sample? because according to the linear equation of Trolox I can calculate ORAC value for each sample using one concentration.

So, to calculate the ORAC value, I need to calculate:

AUC = (0.5 + f1/f0 + f2/f0 + f3/f0 + . . . + fn/f0) x cycle time

Net AUC = AUCSample or standard – AUCBlank

Then,

y (Net AUC) = A. x (concentration) + B

Are steps or procedures of calculation like that or what?

Thanks again hoping to get reply soon.

Mahmoud,

For example, your equation for ORAC is:

y(Net AUC) = 0.27.x(concentration)+4.22

And you found a Net AUC for your sample of 26.68.

Then, you will substitute this value in equation and you will find the result of concentration for umol Trolox per liter (according your informations for Trolox). Don't forget to consider the dilution factor that you used in your samples.

For express the results per gram is necessary to transform. For example, you used 1 gram of sample and extracted with 50 mL of solvent. Thus, you have:

ORAC result umol ----------------1000 mL

                        y-----------------50 mL-----------------------1 gram

Solving the rule of three [y = (Result of ORAC . 50)/1000] you will find your result in umol Trolox per gram.

Best regards

Many thanks Acácio for your help, but you why should I use different concentration from my samples where I will use one one concentration to get one ORAC value of each sample!!!! because I used four sample concentration from each sample according to (HUANG, 2002) method, but in this case I will get four ORAC value if I understand well.

Thanks in advanced.

Stupid