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low boiling point

Robert Preston rapr at med.pitt.edu
Mon Mar 27 12:41:12 EST 1995


forbes at cip.org.ec wrote:
> >We would like to initiate some PCR based methods near Quito,
> >Ecuador at an altitude of 3050 m above sea level.  Water boils
> >here at 89 C which will not allow us to bring the vials up above
> >this temperature.  

Simple capping of the tubes (this is essential anyway, to prevent water
loss by evaporation even in the absence of boiling) will be sufficient to
prevent
boiling at temperatures up to 95-100C or higher.  If your reagents are
pure, and your equipment is clean (and they have to be, if you intend to
do successful PCR) the reactions would probably superheat above the
boiling point even if the
tubes had no caps at all.  Capping will allow pressurization at high temp that
will prevent both superheating and boiling.  BUT, you have to keep those caps
CLOSED despite the pressurization, so plan to add whatever weight you need to
the tops of the tubes to prevent them from popping open.  (which they tend to 
do even in a boiling water bath at sea level, due to the pressure of the
heated air ABOVE the liquid phase!)  Bring a small clothing iron to the
lab, or pour a custom lead (Pb) cap-weight, or use screw-cap tubes (baad
idea, unless you're only doing a few reactions at a time) or best of all,
use a cycler that has a heated-cap/pressure plate assembly, in which case
you would also eliminate the messy oil overlay.

-- 
Robert Preston                                    rapr at med.pitt.edu
University of Pittsburgh                        Pittsburgh PA 15261



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