I want to test the phenol content in my plant sample and I have chosen this method:
"One ml of 20% sodium carbonate solution
was added to 1 ml of the phenolic extract and incubated
for 5 min. at room temperature. Then 0.5 ml of Folin
Ciocalteo phenol reagent (1:1 diluted with distilled water)
was added and incubated for 10 min. at room temperature.
Absorbance of the colored solution was read at 735 nm
using a spectrophotometer".
But I noticed later that most protocols call for an FCR ratio of 1:10 or 10%. Why is that? Is my method reliable or should I change it?
I have come across FCR ratio of 1:10 in some methodologies and I do not think your method is wrong. In my professional opinion, diluting the FCR is merely to have lower absorbance reading. Thus, if you use the same method, but different FCR ratio, you will definitely get different absorbance readings at 735 nm since the FCR are of different concentrations.
What should be of importance to you is expressing the final answer in whatever method you wish to (mg GAE/100 g, etc). So you need to use the same FCR concentration you used on your samples for preparing the calibration curve. If you do this, the results should be statistically close no matter the FCR ratio you have used. The main point is: Maintain the same FCR concentration/ratio for your samples and the calibration curve preparation.
Regards,
Jay
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