Dear all colleagues
We keep working for long time on antioxidant and bioactive properties of plant extracts however we some time miscalculate the accurate values my question is as follow:
We dissolved 2 g sample in 200 mL solvent, then we freeze-dried the extract
1 g of the extract was dissolved in 100 mL
0.2 mL extract was used for the assay of TPC and the absorbance was 0.602.
The standard curve equation was y=0.0005x + 0.039
How to accurately calculate the TPC of the extract and the original sample?
For flavonoids (TFC) we used 0.1 mL extract and the absorbance was 0.111
The equation was y=0.0004x + 0.0281
How to calculate the TFC?
I know that there were many posts about this issue but I need step by step analysis.
I would like to add to the previous question that the standard curves were in ug/mL range
The calculation principle is the same for both TPC and TFC. Firstly, from the measured absorbance and calibration curve you should calculate the concentration in ug/ml: y=0.0005x + 0.039, x=(y-0.039)/0.0005, y=0.602, x=1.126 ug/ml - this is the concentration in extract. Then, the total amount of TPC in 100 ml is 112,6 ug and that is the amount in 1 g of extract. You should know the yield of extract if you want to recalculate on sample basis.
Dear Miona
Thank you very much for your answer
The yield of the extract is 20.34%
Estimation of Total Phenolics:- ( Ref: A.P.I. Part-II, Vol.II, Appendix-5)
Reagents
1. Folin Ciocalteu reagent (1 N): Dilute commercially available Folin-Ciocalteu
reagent (2 N) with an equal volume of distilled water. Transfer it in a brown bottle
and store in a refrigerator (4°C). It should be golden in colour. Do not use it if it
turns olive green.
2. Sodium carbonate (20%): Weigh 40 g sodium carbonate (x 10 H2O), dissolve it in about 150 ml distilled water and make up to 200 ml with distilled water.
3. Standard tannic acid solution (0.1 mg/ml): Dissolve 1 mg in 10 ml of distilled
water (always use a freshly prepared solution). Important: Use standard tannic acid sample (make: Merck) which is found to be the best.
Calibration curve Equation (tannic acid): Y = 0.0324x + 0.0134
Analysis of total phenols
Take suitable aliquots of the tannin-containing extract in test tubes, make up the volume to 0.5 ml with distilled water, and add 0.25 ml of the Folin- Ciocalteu reagent and then 1.25 ml of the sodium carbonate solution. Vortex the tubes and record absorbance at 725 nm after 40 min. Calculate the amount of total phenols as tannic acid equivalent from the above calibration curve equation. Express total phenolic content in (x % w/v).
P.F.A.
Dear Mehta
Thank you for your kind input about the analysis method of polyphenols. The method you provided is clear and sound however the problems that most researcher faced are accurate calculation of TPC and TFC.
Regards
Please use multiple concentrations of standard compound such as gallic acid or quercetin. Then draw a standard curve like y = mx+c, where y is concentration and x is absorbance. Finally, calculate the unknown conc. from the equation.
you will get the content for 0.1ml (According to your experiment), then calculate for 1gm extract and express the result in standard equivalent. eg. 200 mg gallic acid equivalent/ gm extract.
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