filter-sterilized MilliQ water for PCR?

Hiranya Roychowdhury hroychow at NMSU.EDU
Wed Sep 17 11:15:25 EST 1997

At 01:24 AM 9/17/97 -0700, Jun-Ichi Aikawa wrote:
>Clontech recommended to use filter-sterilized MilliQ water for PCR instead
>of autoclaved water, because autoclave can introduce salts. Does anyone use
>filter-sterilized water for PCR? Do I need to worry about its nuclease or
>protease contamination?
>Jun-ichi Aikawa, Ph.D.
>Division of Cellular and Molecular Medicine
>University of California, San Diego

That is strange indeed! Do the Companies want to sell MilliQ water for PCR?
It is true that MilliQ water collected directly off the system will be of
highest quality (reportedly free of even RNases), not because of any filters
but because of the ion-exchange resins that it uses. Not all proteins are
sieved by 0.22u. But we have been using autoclaved water for almost
everything, including PCR, and have never had any problem. Does water vapor
carry salts? If it does then we all have been distilling water for ages for
naught! Maybe somebody from Clonetech can explain. Where do these salts come
from in autoclaved water, unless they are already present in it an/or some
other solution boils over in the autoclave and contaminates the distilled
water sitting beside it. If the autocolave is dirty and the steam valves (in
either direction) do not work propely, there is a possibility that instead
of steady vapor "sprays" will be produced during pressurizing and
depressurizing. But that is a problem with maintenance and not the process
itself. Instead of making these blanket statements, the company reps should
think and qualify them.

Dr. Hiranya Sankar Roychowdhury
Plant Genetic Engineering Lab.
New Mexico State University
Las Cruces, NM 88003
Ph. (505) 646-5785
hroychow at

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