Typically phenolic content is measured using the Folin-Ciocalteau assay and a phenolic acid (such as gallic acid) to set up a calibration curve. The equation you described in the question is accurate (where c = concentration determined from standard curve (mg/ml), V = volume used during the assay (ml), and M = mass of the extract used during the assay (g) and will give GAE in mg/g extract. You'll find various references to the method in literature. Hope that helps.

You should however presenting the results per gram of leaves (fresh weight or dry weight). For this you must know the relationship between the extract and the added mass of the sheet.

Simple and widely used method for the analysis of total phenolic content (TPH) in plant extracts is the Folin-Ciocalteu’s spectrophotometric procedure. Please refer to - Singleton VL, Rossi JA Jr (1965) Colorimetry of total phenolics with phosphomolybdicphosphotungstic acid reagents. Am J Enol Viticult 16:144–158.

Use Folin-Ciocalteu’s spectrophotometric method (GA equivelent) or you can go with HPLC analysis as said above.

Yes all phenolic content can be done by above methods

Folin-Ciocalteu has one drawback, it also reacts with other reducing compounds such as ascorbic acid. This should be taken into account, as described in J Agric Food Chem. 2005;53:1370–3.

It is true that Folin-Ciocalteau assay is a method with some interfering, in the presence of copper it also react with other amino acids, The Lowry method is based on this reaction. However, it is the most used method for quantification of total phenols.

Yes, and that is precisely the interest of the cited method (I am not an author!) ; it compares reactivity to folin before and after a C18 cartridge, and the difference gives the phenolic content (before-after = phenols). This really gives an increased selectivity, which is very relevant in systems such as fruits where interfering compounds may be more abundant than polyphenols.

I agree, the method proposed in the article seems useful for samples containing "high" concentrations of interfering compounds

Total phenolic content was assayed by the Folin–Ciocalteu colorimetric method with slight modification Briefly, aliquots (1.0 mL) of appropriately diluted extracts or standard solutions were mixed with 0.5 mL 0.5 N Folin–Ciocalteu reagent, then the reaction was neutralized with saturated sodium carbonate (75 g/L). The absorbance of the resulting blue color was recorded using a spectrophotometer after incubation for 2 h at 23 °C. A calibration curve was prepared using gallic acid solution. Total phenolics contents were expressed as milligrams of gallic acid equivalent (mg GAE) per 100 g of dry weight.

Determination of total phenolic contents in the plant extracts

The total phenolic content was determined using spectrophotometric method [Singleton VL, Orthofer R, Lamuela RRM. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin-Ciocalteu reagent. Methods Enzymol. 1999; 299:152-178. doi: 10.1016/S0076-6879(99)99017-1.]. The reaction mixture was prepared by mixing 0.5 ml of methanolic solution (1 mg/ml) of extract, 2.5 ml of 10% Folin-Ciocalteu’s reagent dissolved in water and 2.5 ml 7.5% NaHCO3. The samples were incubated at 45 ˚C for 15 min. The absorbance was determined at λmax = 765 nm. The samples were prepared in triplicate and the mean value of absorbance was obtained. Blank was concomitantly prepared, with methanol instead of extract solution.The same procedure was repeated for the gallic acid and the calibration line was construed. The total phenolic content was expressed in terms of gallic acid equivalent (mg of GaA/g of extract).

Sir i need what formula have used in total phenolic content in plant extract.

As said by many researchers, Total phenolic content is most commonly measured by Folin-Ciocalteau assay. Principle involved in assay include oxidation-reduction reaction. We are estimating phenolic content as Gallic acid equiv. But reducing compounds other than Phenols may also react with Gallic acid so it gives wrong results. Though Folin-Ciocalteau assay is most commonly used, some more accurate, economic and robust methods should be highlighted.

Can any body help me in calculation, i have also done total phenolic content by using gallic acid as standard and got 38ppm resullt from GA std curve. but now how to determine the result in mg/g of GA. I have taken 0.050 gram of sample in 10ml of methanol and after etraction i have taken 0.3ml from this and added 2.25ml of follin reagent and then 2.25ml of sodium carbonate.

DETERMINATION OF TOTAL PHENOLICS BY FOLIN-CIOCALTEAU COLORIMETRY

Folin-Ciocalteau (FC) colorimetry is based on a chemical reduction of the reagent, a mixture of tungsten and molybdenum oxides. Singleton adapted this method to wine analysis (Singleton and Rossi, 1965) and has written two major reviews on its use (Singleton, 1974; Singleton et al., 1999). The products of the metal oxide reduction have a blue color that exhibits a broad light absorption with a maximum at 765 nm. The intensity of light absorption at that wavelength is proportional to the concentration of phenols. The FC method has been adopted as the official procedure for total phenolic levels in wine; the Office International de la Vigne et du Vin (OIV), the one international body that certifies specific procedures for wine analysis, accepts the FC method as the standard procedure for total phenolic analysis (OIV, 1990). An earlier variation was the Folin-Denis cedure, but the FC method has displaced it except in a few historical cases of official procedures that have not been updated (AOAC International, 1995).

Cited from (Current Protocols in Food Analytical Chemistry (2002) I1.1.1-I1.1.8

Mr erum dow please reffer this. This may help you https://www.researchgate.net/publication/234109840_Extraction_Purification_Identification_and_Estimation_of_Catechins_from_Camellia_sinensis

Thesis Extraction, Purification, Identification and Estimation of C...

Thanks all for valuable comments. i have done my calculations

 Dear Erum. Please what formular did you use for the calculation. I have gotten the absorbance of my extract mixed with FC reagent. I have also plotted absorbance vs concentration of gallic acid. How do I do the conversion?. The formula stated in the original question, C(GAE)= C*V/M does not make use of the absorbance of the extract.

YA SAME HERE ...The formula stated in the original question, C(GAE)= C*V/M does not make use of the absorbance of the extract.

 What should I do if the mixture of sample, sodium carbonate and FC reagent forms a precipitate or suspended particles after incubation? Can I filter it?

sir same problem is here....i have not any idea regarding value of m...as it is mass of extract used in asssay...if we  take it as stock as i use 1mg/ml...then i use 1ml of different concentration of extract also from 25 microgram/ml to 200 microgram/ml.i.e. i take 25 ul to 200 ul .and reaction mixture after adding all components will be 3.25 ml..

Then using formula 

C1V1=C2V2

0.001X0.025=C2X3.25

C2=0.0000077..and i use it as value of m. in gm.

Is it right or wrong..

Phenolic content is measured via Folin-Ciocalteau assay and a ( Gallic acid) used as phenolic acid standard in calibration curve. This equation is correct

C (GAE) = c x V/M

where:

c = concentration determined from standard curve (mg/ml)

V = volume used during the assay (ml)

M = mass of the extract used during the assay (g) to give GAE in mg/g extract.