Dear Shelley and Gilles,

As Gilles corrrectly explains, the He flow 'stimulate' movement of the
frozen gas. But additionally you have to realize that sublimation of any gas
from a mixture takes more time and also will be less perfect than with a
pure gas. So here the He carrier is working against a complete yield of
trapped gas. Unfortunately, incomplete sublimation and the moving action by
the He causes isotopic fractionation, and one has to check if not too much
fractionation happens if too much of gas is not trapped or moved away by the
He! Just some words of warning. A longer tube indeed helps to reduce this
problem.

Best,
Pier.


> From: Gilles St-Jean <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
> Date: Wed, 28 Jun 2006 10:01:49 -0400
> To: <[log in to unmask]>
> Conversation: [ISOGEOCHEM] automate LN2 trap?
> Subject: Re: [ISOGEOCHEM] automate LN2 trap?
> 
> Hi Shelley
> There are indeed many different trapping techniques as you can see by Willi
> and Pier's comments and references.  Many of the references are from the
> Dual-inlet techniques where the amount of gas is very low and you do not have
> a carrier (e.g. Helium).  The main thing you have to be careful with is the
> fact of the helium carrier's presence.  In some cases we can see (glass trap)
> the frozen gas of interest (e.g. CO2) slowly creep through the trap as the hot
> helium flows through.  The higher the flow, the more heat and carrying
> possiblility of the "ice" sample being fractionated by the "hot wind".  The
> key is in the tubing diameter and it's lenght.  For a fused silica capillary
> (e.g. 0.32 mm ID)in a GC type of flow  (2-3ml/min) it can be relatively short.
> From the EA we tend to have stainless steel 1/6" OD (ID can vary) tubing and
> flows between 80-120ml/min; where thw helium comes out around 60oC.  If you
> make a double loop or spring type trap it should be fine for the lenght !
>  of time you want to trap and release (about 1m lenght should do it).
> 
> As for the trigger to the trap, the ConFlo still has all commands of the 8
> valves available.  You need to find the right wire and add your own solenoid
> with the proper rating(24V, xW)and attach it to a piston onto which your trap
> can be raised or lowered.
> 
> In Isodat you can add this trap to the ConFlo drawing and device, or have it
> as it's own device, and have it available in the Time Events for your method
> which will allow you to automate it.  None of this requires ISL or programming
> knowledge.
> 
> Have fun
> Gilles
> 
> Gilles St-Jean
> Chercheur / Research Scientist
> Université d'Ottawa / University of Ottawa
> Sciences de la Terre / Earth Sciences
> 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5
> Tel: 1-613-562-5800 xt 6830 (Bureau / Office)
>                     xt 6839 (Bureau / Office Lab)
>                     xt 6836 (IRMS lab)
> Téléc. / Fax: 1-613-562-5192
> Courriel / E-mail: [log in to unmask]
> Toile / Web: www.isotope.uottawa.ca
> 
>  
> 
>> -----Message d'origine-----
>> De : Stable Isotope Geochemistry
>> [mailto:[log in to unmask]] De la part de Shelley Kunasek
>> Envoyé : 26 juin 2006 19:14
>> À : [log in to unmask]
>> Objet : [ISOGEOCHEM] automate LN2 trap?
>> 
>> I'd like to automate a continuous flow EA/IRMS system to have
>> a liquid nitrogen trap lower into a dewar and then lift out
>> at the right time.  We'd like to basically build this simple
>> component of a precon or a gas bench without having to buy a
>> whole precon or gas bench.  Has anyone had experience
>> building that type of setup?
>> 
>> Thanks
>> 
>> Shelley Kunasek
>> 
>> University of Washington
>> Department of Earth and Space Sciences
>> 206-543-6223
>> [log in to unmask]
>> 
>