Hello Karine,
We have experienced samples contaminated with ethanol here with our
MultiPrep. We are positive ethanol was the problem as we have changed
the chemistry protocole getting rid of ethanol and got perfect runs
after that. But what we observed on the contaminated samples was
different from what you describe. The mass 46 beam on the sample side
was going sky high, to the point where you could see it on the bargraph
when the sample was admitted in the IRMS, sometimes even saturating the
cup 46. The delta 46 where totally crazy, like several hundreds or
thousands permil.
What you describe looks like contamination. As you say it is very
unlikely that IAEA sent you contaminated NBS19. Have you tried different
batches of acid? Our experience here is that our MultiPrep is usually
crunching excellent carbonate numbers and 100% of the few problems we've
had were due to bad batches of our acid. To see if it is contamination
on the sample side of your system , you might want to load some of your
reference CO2 on the sample side of your inlet through the vacuum line
and admit it all the way back to your MultiPrep , isolate it from the
reference and then admit it on the sample side as if it was a sample and
see if you get this odd behaviour or not and if you get zero when
measured against the reference. You can repeat that trapping your CO2 in
different parts of the sample side and MultiPrep to isolate precisely
where the problem lies.
If you have a contaminated inlet or MultiPrep, you can try to bake it
and see if it cures the problem. Dismantling the MultiPrep valve system
is doable, but not exactly straightforward. If you want to go that way
you have to be sure it really is the problem.
Good luck,
--
François FOUREL
UMR CNRS 5125 PEPS
Université Claude Bernard Lyon 1
2 rue Raphaël Dubois - Bât. Géode
F-69622 VILLEURBANNE Cedex - FRANCE
Tél : +33 (0) 4 72 44 62 42
FAX : +33 (0) 4 72 43 16 88
Email : [log in to unmask]
Karine Charlier a écrit :
> I checked all the parts of the mass spectrometer, the DI and the
> Multiprep and couldn't find a leak.
>
> The last samples I ran were NBS19 from IAEA (from 2 different bottles),
> so I suppose these samples aren't contaminated. However, in order to
> verify this hypothesis, I ran a scan on the sample gas then the
> reference gas by increasing the magnet current from 1.5 to 4 A (so you
> can see peaks of mass 12 to 47 that are in the gas, on the middle
> collector) : the peaks were the same in both gases, with almost the same
> intensities. In case of a contamination by NO2 or ethanol, mass 46 of
> the sample gas should be much higher than mass 46 of the ref gas,
> shouldn't it ?
>
> Karine
>
> Penny Higgins a écrit :
>
>> Hi Katrine,
>>
>> I've had this experience running tooth enamel apatites on a Dual-Inlet
>> system with Multiprep. We finally figured out that it was NO2
>> contamination. This could come from a leak, or could be a
>> contamination of the sample itself. If you've eliminated the
>> possibility of a leak, I have a suggestion to deal with sample
>> contamination.
>>
>> I now run a continuous flow system with a Gas Bench to run carbonates
>> and apatites. ...and we still had poor oxygen (46/44) values with
>> adequate carbon (45/44) values. It turned out that we did, in fact,
>> have a leak that we fixed. Meanwhile, however, we instituted a
>> cleansing protocol for the carbonates. We wash all our carbonates with
>> hydrogen peroxide before analysis (see attached protocol) which has
>> drastically improved our results, despite the leak. I think it's
>> possible that nitrogen, from organics, may be contaminating your
>> sample. Since most DI systems do not employ a GC column, the nitrogen
>> (as NO2) is not separated from the carbon dioxide. My recollection is
>> that NO2 freezes at a temperature very close to that of CO2, and
>> therefore is hard to remove using cryogenic methods. Since NO2 has a
>> mass of 46, it affects oxygen values without hurting carbon values.
>>
>> I hope this helps,
>>
>> ~Penny
>>
>> At 08:27 AM 4/4/2006, you wrote:
>>
>>> Dear Listmembers,
>>>
>>> We recently experienced a problem when carbonates analyses are run on
>>> our Multiprep-Optima :
>>> the 46/44 ratio traces are v-shaped instead of flat,
>>> the 18O precision is bad (around 0.020 instead of lower than 0.008),
>>> and delta18O values of NBS19 can differ from 1 per mil in the same
>>> batch.
>>>
>>> I've checked all the valves of the Dual-Inlet and the Multiprep for
>>> air leaks and cross seat leakage, all the valves are OK.
>>> When I run stabilities and linearities (with the same CO2 gaz in all
>>> the DI), traces are flat and values are close to zero, so the DI
>>> seems to be OK.
>>> I've checked the water trap and the 2 cold fingers for finding
>>> contamination, and there is none.
>>> The bath is equilibrated at 90°C, the needle is brand new.
>>> I've tested 2 different acids, and the result is always the same.
>>>
>>> Have you ever encountered this kind of problem, and found an
>>> explanation ? because I'm running out of ideas now...
>>>
>>> Regards,
>>>
>>> Karine
>>>
>>> --
>>> *********************************************************
>>>
>>> Karine CHARLIER
>>> Environnements et Paleoenvironnements OCeaniques
>>> UMR CNRS 5805 EPOC
>>> Universite Bordeaux I
>>> Avenue des Facultes
>>> 33405 TALENCE Cedex
>>> FRANCE
>>>
>>> Tel : 0 (33) 5 40 00 83 62
>>> Fax : 0 (33) 5 56 84 08 48
>>> E-mail : [log in to unmask]
>>> Web : http://www.epoc.u-bordeaux.fr/
>>>
>>> ********************************************************
>>
>>
>>
>> *******************************************************************
>> Dr. Pennilyn Higgins
>> Research Associate
>>
>> "SIREAL"
>> Stable Isotope Ratios in the Environment Analytical Laboratory
>>
>> Department of Earth and Environmental Sciences
>> University of Rochester
>> 227 Hutchison Hall
>> Rochester, NY 14627
>>
>> [log in to unmask]
>>
>> Office: 209b Hutchison Hall Lab: 209 Hutchison Hall
>> Voice : (585) 275-0601 Outer lab: (585) 273-1405
>> FAX : (585) 244-5689 Inner lab: (585) 273-1397
>>
>> http://www.earth.rochester.edu/SIREAL/index.html
>> *******************************************************************
>>
>
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