phenol/chloro extraction method - (Mar/07/2007 )

Hi, I have a query about extraction methods which I'm sure will be easy to clear up - I just can't seem to find the answer!

I do my RNA and DNA extractions by a phenol (Tris saturated) followed by a phenol:chloroform (50:50 v/v) stage

However, i have heard that it is better to do a phenol/chloroform/IAA (25:24:1) stage followed by a chloroform/IAA (24:1) stage.

Does it actually make any difference - are they just 'different' methods or does one have advantages over the other?

Any info will be very gratefully received.

Cheers.

the IAA is useful in chloroform as stabilizant. So for your preps, it's better if the bottle is old.
second, the chloroform step is for removing the remaining phenol as it's more hydrophobic as phenol.

so a second step phenol chlo IAA should be followed by a chlo / IAA in yor case.
Preferably, use phenol chlo directly.
the question is : why do you need to do a phenol only step ? The answer seems interesting to me.