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Hi Marc

the distance between before and now seems to be the same (about 16 delta 
units for C and 8 for O), if you don't find pollution in the reference 
gases may be that your software lost the calibration delta values in the 
species library and now those values are zero.

hope this helps

Luciano Spaccino


On 25/05/2016 15:37, Marc Davies wrote:
>
> I am analysing C and O isotopes in carbonates using a Multiflow 
> attached to a GV Isoprime IRMS. Recently my  standards have become 
> increasingly more positive (both for C and O), and I can’t seem to 
> isolate the reason why. This has happened over the period of a few 
> days. Last week everything was running fine, and nothing unusual has 
> been done to the instrument in the meantime. Before-hand, however,  we 
> had overheating issues with the compressor, because of leaks in the 
> compressed air line, which were located with snoop and repaired, but I 
> can’t see how this can be related. The measured values for the 
> reference standards has change as follows
>
> Before - *NBS19* -13C = -11, 18O = +8.5. Now - *NBS19* -13C = +5.5, 
> 18O = +16.43
>
> Before - *CO8* - 13C = -18, 18O = -11.5. Now – *CO8* -13C = -2.4, 18O 
> = -3.3
>
> Before –*CO9* - 13C = -58, 18O = -4. Now – *CO9* -13C = -43, 18O = +3.78
>
> I should be grateful if anyone has any idea what might be causing this 
> to happen..
>
> Thanks
>
> Marc
>
> *Dr Marc K Davies*
>
> Senior Technician (Isotope Mass Spectrometry)
>
> School of Geography, Earth and Environmental Sciences,
>
> 118 Fitzroy Building,
>
> Plymouth University,
>
> Drake Circus,
>
> Plymouth PL4 8AA
>
> Office: 01752 584987
>
> Mobile; 07756 176060
>
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-- 
Luciano Spaccino
Istituto di Biologia Agroambientale e Forestale (IBAF)
Consiglio Nazionale delle Ricerche (CNR)
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