Hi Ilya and others,

I have no advise on suppliers, since others living on the same continent
better can tell you where to get it.

There is one matter I like to comment. You mentioned that Conflo is giving
better precision than dual inlet.! I am not convinced that is true,
nevertheless all the small precisions reported. And be careful not to
mention the monitoring gas in a Conflo system as a reference gas - I think
it is a very misleading term that way, giving the impression of what it is
not! It cannot and should not be used as reference - it only checks the
performance of the machine, such as drift or other disturbances that
occasionally may happen, and nothing else (and having a 'fitting' isotopic
composition with the sample values is a bit less critical here than it is
with dual inlet, although it still must not be too different).
Couple of months ago I posted some critical words on this (look in archives)
with an example of carbonate-phosphoric acid digestion systems comparing
off-line dual inlet with on-line-CF single inlet, where in last case
generally smaller precisions are reported, while that cannot be the case
(arguments why were given). I only received one reaction 'off-list', telling
me: you have some arguments there....
On Isogeochem however there was silence! Must be more analysts that are
realizing there is something wrong with this, or does everybody love the
small precisions, and it does not matter how we get them....???

In any case one can state single inlet is NOT more precise than dual inlet,
for the simple reasons of linearity of the machine - I discussed this with
several analysts having large experience with both type of machines, to
check my own understanding on this matter.
The strength of dual inlet always was the direct comparison of an analyte
gas with a reference gas. This is not longer true for single inlet systems,
where indirect comparison is applied, with all related problems to get such
a subsequent comparison.
It must be realized too, that although having a continuous presure in such a
single inlet system, the partial pressure of the analyte gas is changing
continuously in the ion source, whith risk of creating a continuously
changing range of different ions to form over a measurement.

Let me finish to say I like the on-line-CF systems, since it saves a lot of
work and it is helpful to measure smaller samples. But we must be realistic
about the level of precision we really can reach with such a system. It is
not the quality of a CF-IRMS or Conflo, or whatever else is named, I
dispute, also not the delta values as we get, but the reporting of
(unrealistic) precisions (or better combined uncertainties, what it should
be. Is there any advise on this by IUPAC?).

Not what you asked for, but nevertheless I hope it is useful to think about.

Best wishes,
Pier.

> From: Ilya Bindeman <[log in to unmask]>
> Reply-To: Ilya Bindeman <[log in to unmask]>
> Date: Wed, 15 Nov 2006 16:49:22 -0800
> To: <[log in to unmask]>
> Subject: [ISOGEOCHEM] CO and H2 commercial cylinders
> 
> 
> 
> Hello everybody,
> 
> 1) Can we get advice on CO and H2 cylinders  suppliers with geologically
> relevant isotope ratios?
> 
> I have measured two cylinders we have in the building- one from GT&S National
> Specialty gases in Pennsylvania and their values are D/H = ­697 permil for H2
> and ­242 permil d18O and ­459 d13C for CO gas.
> Airgas cylinder was even worse- D/H ­789 permil
> 
> 2) Please comment on how bad these depleted gases will be when running
> unknowns with +20 to ­100 permil range
> 
> I also have Oztech lecture bottles with CO and H2 gases that could be used in
> dual inlet while running samples on our TC/EA coupled with MAT253 in
> continuous flow. I know some labs are taking this route. However I was advised
> to use tanks of H2 and CO and Conflow instead of dual inlet for better
> precision and issues of progressive depletion in bellows.
> 
> 3) We would gladly solicit emails on what other labs are using bellows or
> presurrized cylinders.
> 
> Please reply to the list or directly to me at [log in to unmask]
> 
> Ilya Bindeman and Jim Palandri
> 
> *******************************
> Ilya Bindeman
> Geological Sciences
> 1272 University of Oregon
> 1260 Franklin Blvd
> Eugene OR 97403-1272
> tel 541-346-3817
> fax 541-346-4692 
> 
> 
> 
>