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27-29 September 2023, University of Bayreuth (UBT)

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What is a typical GC-IRMS performance? Long-term records of backgrounds, linearity, sensitivity, precision, and trueness on different GC-IRMS instruments

Felix Antritter1, Martin Elsner
1 IWC, TU München

P 5.3 in Methods, Models, Standards

F. Antritter1,*, and M. Elsner1

*presenting author: felix.antritter@tum.de

Gas chromatography - isotope ratio (monitoring) mass spectrometry instruments are installed with specifications on quality assurance parameters, and these parameters are regularly monitored in routine operation. Backgrounds in morning tests are recorded to inform about the leak-tightness of a system. The amplitude of monitoring gas pulses or air injections is an indicator of the sensitivity of the mass detector. Monitoring gas pulses are introduced at different amounts to test for linearity meaning that resultant isotope measurements should ideally be amount-independent. The standard deviation of isotope values informs about the precision of isotope analysis.

In addition, laboratories need to purchase external reference materials and establish a set of in-house standards to ensure the trueness of target compound analysis over days, months, years, and decades. Long-term performance data over these time scales, however, are rare. While the precision of GC-IRMS analysis is typically specified as ±0.2‰ to ±0.3‰, and total uncertainty including both precision and trueness is indicated as ±0.5‰, publications on systematic data on long-term performance are seldom.

Here we will share such quality assurance data over more than 10 years from three different GC-IRMS instruments in our laboratory. We would like to stimulate an exchange with other labs of experience and best practice.

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