Hello ;

I found the details of Folin-Ciocalteu reaction, and the exact reason of choosing Gallic acid as a standard...

the reasons are: Partly for historical reasons, In addition it is inexpensive, soluble in water, recrystallized easily from water, readily dried, and stable in the dry form.

so I think that there isn't a general rule but every standard has different reasons for choosing it.

Dear Maysoon,

The Folin-Ciocalteu reagent (FCR) or Folin's phenol reagent or Folin-Denis reagent, also called the Gallic Acid Equivalence method (GAE) is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric assay of phenolic and polyphenolic antioxidants

this reagent does not only measure total phenols and will react with any reducing substance. The reagent therefore measures the total reducing capacity of a sample, not just the level of phenolic compounds.

This reagent forms part of the Lowry protein assay and will also react with some nitrogen-containing compounds such as hydroxylamine and guanidine.The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base guanine, the trioses glyceraldehyde and dihydroxyacetone, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent

-------------------------------------therefore

The method developed for total phenol determination even though it is having less selectivity and specificity (as it is reacting not only phenols)

Gallic acid has been used as calibration standard and the total phenols has been reported as galic acid equivalent as the method is developed so.

you need to report your phenol standard equivalent and validate a method if you want to use any other phenol as calibration standard.

reference:

http://en.wikipedia.org/wiki/Folin-Ciocalteu_reagent

Regards

Selvan

Thanks Selvan ,

but I already know most of that.

anyway, if I may rephrase the question: on what basis do we choose ANY standard to be standard in the calibration curve? is it because it has the highest concentration in the sample (for example) or what?

And I have another question -since you know about the Folin reagent- : in Folin-Ciocalteau assay ,what 's the reaction mechanism (in details if possible) and how do we get over interferes?

thanks again,

Maysoon

-------------------------------------

PS: my Prof. doesn't want me to use Wiki as reference.... I'll be grateful if you have another one!!

Hello ;

I found the details of Folin-Ciocalteu reaction, and the exact reason of choosing Gallic acid as a standard...

the reasons are: Partly for historical reasons, In addition it is inexpensive, soluble in water, recrystallized easily from water, readily dried, and stable in the dry form.

so I think that there isn't a general rule but every standard has different reasons for choosing it.

I think the reason that gallic acid is used is simply that it is nonvolatile (MP 253 °C with decomposition, BP not given). Phenol itself, and most substituted phenols, have relatively low melting and boiling points. Check in CRC Handbook of Chemistry and Physics for full data.

The other point is that phenol is fairly unpleasant to use and best avoided if possible.

Thanks a lot for your concern, but as I said before I already got most of the answer :)

I'm still looking for the mechanism though, dose anyone know it?

Hello M. Al-Hafez

I think the following article might be helpful. Also you can

study literature cited in this article.

J Agric Food Chem. 2010 Jul 28; 58(14): 8139–8144.