(none)

tfitzwater at NEXSTAR.COM tfitzwater at NEXSTAR.COM
Wed Nov 4 16:27:25 EST 1998


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How to pH phenol

Organics such as phenol and chloroform have much lower dielectric constants
than  water.   The  very large liquid junction potential can cause problems
such  as  pH  drift, long stabilization times and pH electrode damage.  The
indicator  chemical  in  pH  paper   is  destroyed  by  phenol resulting in
inaccurate  pH  measurement.   In  order  to  accurately  measure the pH of
saturated  phenol  it  is  necessary to solubolize the phenol in an aqueous
medium.

How to pH Tris
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=AE-buffered Phenol

For  saturated  phenol  (no  chloroform),  mix 2 ml organic phase with =
5 ml
methanol and 13 ml water and pH entire sample.  pH will drift down over=
 the
course  of  about 30 seconds until it stabilizes.  (This method is from=
 the
Ambion 1994 catalog.)

How to pH Tris=AE-buffered Phenol/Chloroform

For  phenol:chloroform  or  acid phenol:chloroform, mix 2 ml of the org=
anic
phase with 8 ml methanol and 10 ml water.  Mix and measure pH of the en=
tire
sample  with the pH electrode.  pH will drift down over the course of a=
bout
30 seconds until it stabilizes.

pH  measurements of solubolized and unmodified phenol and phenol-chloro=
form
mixtures.
E. Kleinhenz and S. Cohen 1991 BioTechniques 10 (6) 740-741.  (Amresco)=

The electrode used was a Calomel reference electrode (mercury/mercuric =
acid
reference  cell  type)  obtained  from  Cole-Parmer  (Chicago,  IL) mod=
el #
L-05669-20.   Silver/silver  chloride  type  electrodes are not recomme=
nded
because  they  do  not  accurately  measure  the  pH  of  Tris=AE.  Sin=
ce the
electrode  dehydrates  during phenol testing, it should be soaked in Ty=
pe I
water to rejuvenate the glass bulb.

It is much easier to buy prepared phenol and phenol:chloroform.

Tim Fitzwater
Principal Research Assocoate
NeXstar Pharmaceuticals


From: genet at public.sj.he.cn ("Bethune international peace hospital")
Subject: help about equilibrate phenol
Date: 2 Nov 1998 18:51:08 -0800

Hi
How to equilibrate phenol to a PH>7.8?
We have equilibrate phenol for one week with Tris.Cl(1M,PH8.0),
but the PH of penol phase is still under 7.0 and much phenol lose.
thank you for help
responds to:
genet at public.sj.he.cn



=

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