Stable Isotope Geochemistry


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Paul Brooks <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Wed, 18 Feb 2004 14:43:38 -0800
text/plain (196 lines)

I went through the ordeal of adding CO reference gas to our lab several
years ago and wrote in my experiences, copied below.  I have now updated
them with my latest experience.

In our case there was a great deal of difference in the alarms required
depending on the size of tank that was stored or used in the lab.

Note in item #8 below that the rate of CO use with a Conflo II is very low
if the vent capillary on the regulator is plugged.

1) Get the health and safety officer involved early.  At our institution
orders for CO have to go over his desk and be signed.  This may mean there
is a delay of several week while it is on his desk.  This delay is after he
has approved the plan for the lab, and after a delay while he and the user
schedule a time to tour the lab.

2) We were allowed to keep a cylinder of CO in a chemical fume hood
provided the hood has an alarm that goes off if the hood flow goes
down.  This means we have had to order a small 33 cubic feet cylinder from
MG industries that will fit in the hood. This cylinder needed custom
filling and so was delayed another few weeks.  An advantage of using a
small cylinder is that the requirements for alarms for the room/building my
be very different.

3) We could not readily use the bellows for the CO as a standard as we
could not store a large CO cylinder outside (fears someone could get a face
full of CO while filling another container). It still had to go in a hood,
so we might as well use it directly as a standard.  Originally I only
considered buying a cylinder of at least this size, but in hindsight we
could have kept one small reference tank in the lab and just used it to
re-fill the sample bellows as Gilles suggests.  The safety officer had
measured the room and then specified what size tank we could have and not
have it in a hood.  I forget the size, but it was a few liters of gas, but
would have been adequate for filling a reference bellows.

4) The standard line from the cylinder passes from the hood along a 1/16
inch stainless steel tube but this has to be contained in a 1/4 inch copper
(or equivalent) tube which is under negative pressure in the hood.

5) The safety office suggested we simply run a PVC pipe to vent our Conflo
II to the hood, but this was not approved by the fire marshal, so make sure
fire marshal approval is given before starting a plan.  We were able to put
in 3" aluminum flexible pipe which was easier to install than PVC
anyway.  The mass spectrometer pumps are also vented into the hood.  So
make sure all safety people have been consulted!!

6) California OSHA requirements now specify a background of no more than 25
ppm CO for an 8 hour work day.  This is more stringent than  USA Federal
regulations and I was not even able to find a monitor/alarm that advertised
it would record this low.  All the home use CO monitors that sell for
US$30-100 in regular hardware stores specifically say in small print "does
not meet OSHA safety regulations".  Our safety office approved one of these
domestic alarms (!), but our director would not as he pointed out that we would
be fined if we had an OSHA inspection.  I a Toxi Plus single gas detector
from Biosystems inc.
that is US$500 that has been excellent, although it took several weeks to
get, another delay.  I was required to order the calibration kit with it,
but it has only been out of calibration once in 2 years.  Placement
of the alarm did not seem to be a major consideration.  Some have suggested
where people are sitting, others at the Conflo II itself.

7) Attempting to connect up the 3 inch bent directly too the Conflo II
produced a noisier 30/28 ratio, as others have mentioned.  I eventually
screwed on a 3 inch diameter flange onto the top of the Conflow II vent
hole, and then used a 4 inch to 3 inch adapter above this to form a little
hood over the Conflo II vent hole and new flange.  The result is quite a
draft up the little hood that apparently sucks enough air through the
Conflo II to keep CO moving through the system, but does not allow it to
build up, at least as measured by a domestic CO monitor.  The 30/28 ratio
is now quite steady.  My Conflo II has a small 1 cm diameter hole to the
right rear of the cover that must allow air in.  See also #8 below.

8)   The regulator that supplies the reference CO in my Conflo II
has two capillaries attached.  One goes to the mass spectrometer inlet, the
other vents the regulator.  While taking the FM class in Bremen, the
instructor suggested we decide on the pressure we needed for the reference
gas, let the system equilibrate (I assume for a period of hours), and then
block the vent capillary with a GC septa.  I have done this and the rate of
CO use has been reduced to a very low rate, from the 33 cu ft tank, I have
only used about 1/4 in 2 years.  This may explain why I don't see any CO
around the Conflo II.

9) We are required to post notices on the lab doors that say CO is in use
in the lab, and the lab must be evacuated if the CO alarms go off.  All
personnel working in the lab must be instructed that CO is in use, and to
leave the lab immediately if the CO alarm goes off.  Based on some of our
previous experience, one can imagine a student working late at night in the
lab who gets annoyed by what appears to be a malfunctioning smoke detector
(since the CO alarms look like smoke detectors), and might simply remove
the batteries if they do not realize what the alarm is doing!!  A
disturbing thought.

Thanks again for all suggestions on setting up for CO.

Paul Brooks.

At 11:24 AM 2/17/04 -0500, you wrote:
>I will second what Gilles said about the dual inlet for CO. We've been
>using this method for running the TC/EA for nearly two years with excellent
>results. The only thing to be cautious of is that you start each run with a
>fresh aliquot of reference CO set up so that with the bellow fully
>expanded, you have close to the maximum usable voltage signal. That way,
>any gas depletion and isotopic drift during the run will be minimized. You
>can refill the bellow to the appropriate pressure (about 80 mBar for us)
>probably hundreds of times  with a lecture bottle, using the dual inlet
>valves to introduce and equilibrate a small volume from the bottle. We will
>refill the lecture bottle when needed from a large tank of Messer CO stored
>inside a fume hood.
>At 08:50 AM 2/17/2004 +0100, you wrote:
>>Dear list members,
>>We are in the process of setting up a CF-IRMS system (Delta + XP, gas bench,
>>TC-EA and flash EA) in our laboratory. We are somewhat uncertain as to the
>>best design for the CO gas suppyling system, in terms of efficiency and
>>If you have gone through this as well, we would like to hear about your
>>choices in terms of storage of CO tank (inside, outside, security
>>locker....), as well as tubing, vannes and purging system for the gas
>>delivery line. We presently have a quotation from a major gas supplier which
>>is outrageously expensive and we are looking for less costy, but fully
>>secure, alternatives.
>>Please, reply directly to me at [log in to unmask]
>>Jean-Pierre Girard
>>Isotope Geochemistry Unit
>>3 avenue C. Guillemin - BP 6009
>>45060 Orléans cedex 2 - France
>>Tél. : - Fax :
>>e-mail : [log in to unmask] - web : <>
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>Jonathan D. Karr, Ph.D.
>Technical Director, Duke EnVironmental stable Isotope Laboratory (DEVIL)
>Duke University Dept.of Biology & Nicholas School of the Environment and
>Earth Sciences
>National Phytotron, Box 90340
>Durham, NC 27708-0340
>(919) 660-7418
>Fax: (919) 660-7425
>[log in to unmask]
>laboratory website:
>Adversity is an opportunity

Paul D. Brooks,
Center for Stable Isotope Biogeochemistry,
Dept. Integrative Biology MC3140,
3060 Valley Life Sciences Building,
UC Berkeley, Ca. 94720-3140.

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