Re: ORGLIST: Folin-Denis reagent

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From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Wed May 16 2001 - 05:32:47 EDT


Dear colleagues,

In reponse to the inquiries of some of you, here's the summary of the
replies I've got on the Folin-Denis reagent.

All the best,

Jacob

1. From: Erik-Jan Ras <ej_ras$##$yahoo.com>

Total Phenolics and Proanthocyanidins:

Initial extract
To each test tube add 30mg of dry finely ground plant material. Add 10ml of
50% aqueaous ethanol or methanol and extract for two hours shaking every 15
minutes (vortex). After samples have cooled and settled, pipet off 5ml and
save for analysis.

Standards
Tannic acid (CAS 1401-55-4) for total; use about 10mg, and 100 - 600l for
a curve. 600l represents 6mg of total phenolics, more than this becomes
non-linear. Metrosideros extract (SH) for proanthocyanidins; dissolve about
5mg into 10ml of extracting solution for a stock standard. Dilute
100/200/400 and 800l of stock to 1ml of extracting solution for a curve.

For total phenolics
Add 200l of initial extract to a 50ml volumetric flask containing about
25ml of water. At time 0 add 2.5ml of Folin-Denise reagent and mix well.
After 3 minutes add 5ml of saturated sodium carbonate and bring to volume
with water; mix well. After exactly 20 minutes, measure the absorbance at
760nm

For Proanthocyanidins
Add 1.0ml initial extract to a test tube. Add 10ml of the n-butanol-HCL
reagent and mix well (vortex). Place on dry bath at 100C for 1 hour. Let
cool and measure absorption at 550nm

Folin-Denis reagent:
To 750ml water add 100g sodium tungstate and 20g phosphomolybdic acid to a
2L flask. Add 50ml orthophosphoric acid. Reflux for 2h. Allow to cool and
make upto 1L. Store in dark.

n-butanol-HCL reagent
Dissolve .7g ferrous sulfate heptahydrate in 25ml HCL and a little
n-butanol. Then dilute to 1L with n-butanol.

Saturated Sodium carbonate
Dissolve 350g sodium carbonate/1l water at 70-80C

 reference for Folin-Denise reagent and Saturated Sodium carbonate;
Official Methods of Analysis of the AOAC, Seventh edition, 1950

reference for n-butanol-HCL reagent; S. Mole and PG Waterman, A critical
analysis of techniques for measuring tannins in ecological studies.,
Oecologia 1987 72:137-147

2. From: Eugene Leitl <Eugene.Leitl$##$lrz.uni-muenchen.de>

Have you tried:
http://www.google.de/search?q=folin-denis+reagent&hl=de&meta=

3. From: Derek McPhee <djmcphee$##$sympatico.ca>

Colorimetirc reagent for phenolics, apparently popular among the soil
research folks. For reagent recipe and procedure see for example
http://www.stanford.edu/group/Vitousek/folin.html



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