question about phenol/water saturated solution

Z.L. K via (by athelas0113 from
Fri Feb 8 21:17:04 EST 2008

Hi all,
I have a question with regard to the phenol/water saturated solution. I
didn't add any acids into it when i made it, when i test the pH of the
aqueous phase it said below 5 with the pH paper. the phenol was a fresh one
from some commercial company back then. currently the pH of the aqueous
phase is still the same after half a year sitting in the cold room at 4 C.
Today my labmate brought up a question for me and asked me what acid I added
into to to bring down the phenol solution pH. I told him I didn't add
anything. based on my understanding from reading online literatures before,
phenol is an organic acid and its pH stays low unless you use some buffer to
bring it up to the point you want it to be (such as pH 7 for extracting
DNA). I wonder if my understanding is correct or not, as i couldn't find any
detail online information now, which is weird.

My question here then should include two parts: 1, i have had RNA extracted
with this phenol/water saturated buffer (well then it's from the in vitro
transcription reaction, quite pure an RNA yield anyway), does it mean that
the water-saturated phenol really has the right pH to extract RNA (just to
answer my labmate's question); 2, if not, what acid should be used in
adjusting the pH?



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