Dear Uli,


Which GC/C-IRMS system do you use (i.e. Europa, Finnigan,
Micromass)?

> what's the usual consumption of He for a GC/C/IRMS device? We seperated
> our machine from the common gas supply of the laboratory five weeks
> ago. Within that time span it ate the content of one 50l tank. Is this
> normal?
>
> My GC is working at a headpressure of ~25psi and the combustion interface
> is kept more or less at the same value. The major connections to the GC
> and to the interface seem to be leak free.

25psi column head pressure? That sounds a tat excessive. What
kind of column do you use (dimensions, film thickness)? Optimum
linear velocity for He is about 28 to 32 cm/s (or 1.0 ml/min give or
take 0.2), which translates to something like 8 to 14 psi (at 70 C)
for columns with an internal diameter of 0.32mm and 0.25mm,
respectively.

> I know its all depending on the length and diameter of the capillaries
> that are in use, and I guess there are a lot of differences between
> various applications. It is just that I want to get a rough idea of the
> order of magnitude.

On a Delta(plus)XL, a standard He cylinder (180 - 200 bar when full)
should last you about 5 months.

For the aforementioned column head pressures, a He backflush
(interface) pressure of about 20 psi is more than ample.


Hope this help.


Best wishes,

                      Wolfram





***********************************
Dr. W. Meier-Augenstein, CChem, MRSC
Senior Research Fellow

University of Dundee
School of Life Sciences
Division of Molecular Physiology
Old Medical School, Small's Wynd
DUNDEE  DD1 4HN


Tel.: +44-(0)1382-34/5124, /4574, /4968
Fax:  +44-(0)1382-34/5514

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URL1: http://www.dundee.ac.uk/biocentre/SLSBDIV6wma.htm
URL2: http://www.dundee.ac.uk/anatphys/wma/meieraug.htm
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