Dear All,

We have an EA-Conflo III-IRMS (ThermoFinnigan 
Deltaplus Advantage) system for carbon & nitrogen isotope determination.  

Recently, we have been dealing with graphite samples, which have an 
enormous high CN ratio. That means, a very large sample size is required to 
put into the combustion chamber in order to obtain nitrogen isotope value.  
Theoretically speaking, the GC column that comes after the reduction 
chamber will separate the N and C signals. However, in the case of an 
incomplete combustion, if any, due to the large sample size we put it, 
would there be an overlap of CO with N2, since both have a mass of 28?  
Increasing the time on the oxygen injection is one way to prevent 
incomplete combustion. However, we are not sure if the nitrogen signal we 
obtained is purely nitrogen or a mixture of Co and N2. Maybe someone can 
shed us some light on this matter. Thank you very much!!!

Best Regrads,
Jean

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Jean Chen
Research Assistant
Research Center for Environmental Changes
Academia Sinica
Taipei, Taiwan
email: [log in to unmask]