Stable Isotope Geochemistry


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"Wassenaar,Len [NHRC]" <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Wed, 18 Feb 2004 10:00:18 -0600
text/plain (80 lines)

1. We use an Isoprime for CO - in our case we use a dual inlet system for
CO/H2/SO2 reference gas injections rather than a ref gas box. We only use
our ref gas box for CO2/N2.  Gilles in an earlier posting gave many good
reasons why one ought to use a dual inlet for the nasty gases, cost and
weird isotopic values not withstanding.  The ref gas boxes (from all
manufacturer?) have a fairly constant continuous flow of the gas (CO or
otherwise) that vent into the lab air by default, far greater than the bleed
from a dual inlet waste flow.  No matter which route you choose you will
want to properly vent all your IRMS roughing pumps and ref box bleed valves
to a fume hood and install a CO detector. The level and cost of security
required will depend on the health and safety rules in your organization.

2. This is very easy - you simply tell the software which system (bellows,
ref box) you are using for your reference pulse source.  All of this is
already set up in Masslynx for Isoprime. There is nothing fancy about this
this approach, which has been used since the early 1990s. Personally I like
the dual inlet bellows injection system better as its less wasteful and more
flexible, although its more expensive to buy initially.

However, I still do not really understand why anyone would want to use CO
for measuring 18O in water over so easily automated CO2-water equilibration,
and especially so for salty to more saline samples (ie 18O activity verus
concentration).  Never got a good answer to this question on this list
before, and haven't seen a slam dunk paper in the literature yet.
Anecdotally, I hear nothing but complaining from labs who tried to use CO
for 18O in waters (very poor precisions, huge memory effects, on and on). So
why even bother?


Leonard I. Wassenaar, Ph.D.
Environment Canada
11 Innovation Blvd.
Saskatoon, SK
Canada, S7N 3H5
tel: 306-975-5747
fax: 306-975-5143

-----Original Message-----
From: H.A.J. Meijer [mailto:[log in to unmask]]
Sent: Wednesday, February 18, 2004 8:22 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] CO gas for CF-IRMS

Dear Colleagues,

The question by Jean-Pierre Girard and the following discussion is most
interesting to me, as we are in the process of buying a GVI Isoprome.
Originally it was intended to be just for 2H of water, but presently we are
discussing the extension to 18O as well. And that brings us into the CO
buisiness. I did not realise these security problems before, and the
discussion brings me to some questions:

(1) Why would the CF use of the Isoprime (or the Finnigan equivalent) use
more CO than the dual inlet? After all it is just the short reference pulse
each time that uses the gas?
(2) How can you run a dual inlet system in combination with elemental
analyser  combustion/pyrolysis? Or do you just use the dual inlet
arrangement as a smart kind of reference gas injector?
(3) Did anyone try CO2 (with about 8% of CO+ formed in the source) or even
enriched N2 (with 15N15N added) as a substitute for CO?


Harro Meijer


Prof. dr. Harro A.J. Meijer
Centrum voor IsotopenOnderzoek (CIO), Rijksuniversiteit Groningen Nijenborgh
4, 9747 AG  Groningen, Netherlands
tel +31-50-3634760   fax +31-50-3634738