Buffering Phenol

Jim Owens jow at helix.nih.gov
Thu Jun 9 07:55:22 EST 1994


In article <2t4u1u$pe5 at mserv1.dl.ac.uk> Dr. C.J. Chan, cchan at crc.ac.uk
writes:
>I have the same problem when I tried to buffer some phenol myself. I
just 
>cannot get the pH to 8 and when I add NaOH, the whole thing goes into a
single
>phase. If someone knows why and how to solve this problem, please let 
>me know.

This has never happened to me.  What I do is add an equal volume of 0.1M
TrisHCl, pH 8.3, to the phenol and three drops of 5M NaOH from a Pasteur
pipet.  The other people in our lab just add Tris base and water to the
phenol, and no one has a problem with there only being one phase.

Just make sure the aqueous, upper phase has a pH over 7.5 and less than
9.5 to make sure DNA and RNA remain in the aqueous phase of the phenol
extraction and will not be degraded.

My guess for the phenol dissolving in the aqueous phase:  Phenol is a
weak acid.  If titrated with NaOH it will become sodium phenolate which
should be somewhat soluble in water.

Good luck,

Jim Owens



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