Usually a standard curve from 0 to 200 mg/L works good,, with gallic, chlorogenic and ferulic acid since the absorbance of the máximum point is between 0.6 and 0.7.

You can check this paper for protocol of phenolics and antioxidant capacity assays

https://www.researchgate.net/publication/308135799_Chickpea_Cicer_arietinum_and_Soybean_Glycine_max_Hulls_Byproducts_with_Potential_Use_as_a_Source_of_High_Value-Added_Food_Products

Regards.

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Interesting Mr. Guillermo. I have some doubt, some papers about phenolic content show concentrations for a standard curve of gallic acid like: (1) 1.57 ug - 15.7 ug,  (2) 0 - 10 mg/ml, (3) 0 - 165 mg/L, (4) 0.05 - 0.40 mg/ml, and finally (5) 0 - 500 mg/L from the professor Aly R.

Would you say this concentration range (0 - 200 mg/L) is recommended to quantify phenolics in leaves anyway? Well, you worked with chickpea and soybean hulls. 

I worked with a concentration range of 0-150ug/ml and I had an OD rannge of 0.1-0.6

N.B: I used 6 different plants

Hello Dear Halima

It seems that concentration must be prepared in order to obtain an adequate range between 0.2 - 0.7. It means that concentrations could vary, for example, 0 - 200 mg/L, 0 - 500 mg/L, or 0 - 150 mg/L like yours, as long as range is optimum.

Thank you for your answer.

Regards