ah ok, so then i have only few ideas left. Baking the trap is very
important to get rid of blanks, but you did that. Are you using silver
capsules? Tin has a large CO blank, too.
Not related to the CO blank, but the peak height of your samples will
also have large influence on reproducibility. The isoprime is very
nonlinear for d18O in the low and middle (0 to 13 nA) peak height
range. You need high peaks for d18O (>13 nA, better >15 nA) to get
into the linear range and thus get good reproducibility (this was
confirmed by Elementar and seems to be an issue for all isoprimes).
You would also see that in a reference gas test. Because of that, your
reference gas pulse should also be high (e.g. 16 nA)!
I hope you will find something and believe me i can feel your pain... :-)
Zitat von B Jones <[log in to unmask]>:
> Hi Marc,
> Thanks for the info and response.
> It seems I neglected to include an important part of the name of the EA. It
> is a Vario Pyro Cube, sorry for providing misleading details. I did not
> realize there were so many variants.
> I am using the High temp technique (ractor at 1450C) with the glassy carbon
> tube filled with lamp or carbon black/glassy carbon chips and have tried
> following the manual in high detail, but still get this CO production.
> I will try and investigate gas contamination issues as suggested by other
> Thanks again.
> On Thu, Mar 7, 2013 at 3:50 PM, Marc Ruppenthal <
> [log in to unmask]> wrote:
>> Hi Brian,
>> You will have difficulties with a vario cube for two reasons:
>> 1) It cannot go above 1350°C. Using the PyroCube I only get good d18O
>> values in excess of 1400°C. I know that Elementar has published a guideline
>> (or paper?) saying it is possible at lower temperatures also with the vario
>> cube (which is reasonable based on theoretical considerations, Schuetze
>> Unterzaucher reaction theoretically works at ~1100°C), but it is not
>> working for me either below 1400°C despite otherwise optimal reactor
>> conditions (glassy C tube filled with carbon black).
>> 2) You cannot use a glassy C tube with the vario cube. You have to use
>> quartz or ceramics, and putting quartz or ceramics in contact with glassy C
>> or carbon black at temperatures above ~1300°C will create a really huge CO
>> blank. It is exactly as you describe it: The CO background is continuously
>> collected in the trap and creates a mass 28 peak when released from the
>> Your problems would disappear when using high temperature conversion AND a
>> glassy C (or SiC) tube...
>> Best regards,
>> Zitat von B Jones <[log in to unmask]>:
>> HI ,
>>> I am attempting to analyze oxygen isotopes (as CO from HT pyrolysis) in
>>> solids using a Vario cube connected to an Isoprime. I have tried a few
>>> different reactor packings, multiple method and trap temp settings, many
>>> trap bakes, many hours of reactor conditioning, and about everything I can
>>> think of but the reproducibility is on the order of 50 per mill on benzoic
>>> acid standard. I have discovered that running true blanks (nothing dropped
>>> into reactor) gives a very nice and consistent 3nA peak (mass 28)! EA
>>> passes leak test in rough and fine modes and the sample flush flow is set
>>> to 90ml/min for 60s. The N2 peak (during its N2 background time) has
>>> minimal baseline change, so I do not expect this is my 3nA peak. If the EA
>>> is allowed to sit idle and trap at 40C this CO peak grows much larger, but
>>> always comes back down to the 3nA level after 3-4 run cycles.
>>> I have completely run out of ideas and am wondering if this analysis is
>>> even possible on this EA. Is there anyone out there who has managed to get
>>> d18O methods to work on the vario cube and, if so, would you be willing to
>>> share your secrets?
>>> Any ideas or advice is greatly appreciated.
>>> Brian Jones
>> Dipl.-Geograph Marc Ruppenthal
>> AG Prof. Dr. Yvonne Oelmann
>> Eberhard Karls Universitaet Tuebingen
>> Forschungsbereich Geographie
>> Ruemelinstraße 19-23
>> 72070 Tuebingen
>> Raum: W505
>> Tel.: +49 (0) 7071 29 77527
>> Mobil: +49 (0) 176 96810834
>> E-Mail: [log in to unmask]**de<[log in to unmask]>
> Brian Jones
Dipl.-Geograph Marc Ruppenthal
AG Prof. Dr. Yvonne Oelmann
Eberhard Karls Universitaet Tuebingen
Tel.: +49 (0) 7071 29 77527
Mobil: +49 (0) 176 96810834
E-Mail: [log in to unmask]