Help with He sparging in HPLC

Tom Thatcher ttha at uhura.cc.rochester.edu
Tue Feb 13 09:04:53 EST 1996


In <4fog9u$d55 at newsbf02.news.aol.com> jafinlay at aol.com (Jafinlay) writes:

>I use helium sparging in our HPLC solvents to degas.  I have yet to find a
>good text explaining exactly how this works.  Does anyone out there know
>of good documentation on He sparging of solvents?  If not does anyone know
>of any more chemistry/chromatography related newsgroups?

>Judith Finlay

Judith,

a liquid can only hold so much dissolved gas.  If you use unsparged HPLC
solvents, they are air-saturated.  The solvent going into the column may
be at 500 psi or higher, which keeps the gas in solution.  At the column 
outflow the pressure may only be a few psi (whatever the backpressure 
of the UV flow cell).  This sudden pressure drop can cause the dissolved 
gas to come out of solution and form bubbles between the column and
detector, which can screw up the readings from the detector.  This is 
the same principle as the "bends" when a diver who rises suddenly to the 
surface develops bubbles of nitrogen in his bloodstream.

When you sparge with helium, the helium displaces all the other gases
dissolved in the solvent so that the solvent is helium-saturated.  But 
helium is so small and mobile that it easily diffuses through the plastic
intake tubing between the solvent reservoir and the pump.  The solvent 
that reaches the pump head then has no dissolved gases at all, so you get
no problems with bubbles between the column and detector.

-- 
Tom Thatcher                          | You can give a PC to a Homo habilis,
University of Rochester Cancer Center | and he'll use it, but he'll use it
ttha at uhura.cc.rochester.edu           | to crack nuts.



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