I am not familiar with this system so this may be of limited help. When I observed such a thing on a Thermo TC/EA with liquid injection this was related to the syringe that consistently injected different amount of waters due to malfunction. However, there was no scatter - instead I the syringe had kind of two stages with two very different peak heights and therefore two different isotope data (one correct, one false). Since you run solids this may not be the case here.
However, you may check the autosampler for proper function. I don't how the transfer from the sampler into the reactor is done. If there is kind of a helium flushed "turn over" system you may also check this.
Also I assume that the standards are all prepared in the same batch by the same person? We once had every second NBS 19 giving no signal on a gasbench and it turned out than one student weighed in something else and two batches were nicely mixed in a rack with the organic powder on every second position...
Am 02.03.2013 um 14:10 schrieb Marc Ruppenthal:
> Dear isogeochemists,
> I am seeing very strange behavior of our PyroCube coupled to an isoprime IRMS:
> Systematically, EVERY SECOND deltaD value I measure for IAEA-CH-7 (at the moment used as a test for operational readiness of the machine) is accurate whereas one value in between two accurate ones is always off, sometimes by ten permil, sometimes by 20 or 30 permil (too positive).
> I am using a ceramics reactor filled with glassy C chips operated at 1360 °C (has always worked in the past). I have already checked the usual suspects for malfunction (temperature, flow, leaks) but could not find anything.
> Has anybody seen something like this before or does anybody have any suggestions what could cause such a pattern? I would be very happy to receive some suggestions because I have a hard time figuring out how this can be...it is weird...
> Thank you very much in advance for your help and effort!!!
> Best regards,
> Dipl.-Geograph Marc Ruppenthal
> AG Prof. Dr. Yvonne Oelmann
> Eberhard Karls Universitaet Tuebingen
> Forschungsbereich Geographie
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> 72070 Tuebingen
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Dr. Robert van Geldern
GeoZentrum Nordbayern / Applied Geosciences
University of Erlangen-Nuremberg
91054 Erlangen, Germany
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