Measurement of C and N isotopes of geological samples using Delta V Plus Stable Isotope Ratio Mass Spectrometer via different preparatory systems

Abstract

Stable isotope studies have proven their unique potential in unraveling several key biogeochemical processes occurring on solid earth as well as in world oceans. In addition, measurements of stable isotopes of lighter elements viz. C, N, O have provided several hitherto insights to fundament natural processes capable of impacting global climate ranging from seasonal to orbital timescales. Understanding a ‘biogeochemical’ process using isotopic tracers is profoundly dependent on quality of isotopic data generated using stable isotope ratio mass spectrometer (IRMS). Exact determination of accuracies and precisions achievable in a given laboratory condition greatly contribute correct interpretation of the isotopic data. We present here standardization of newly acquired IRMS (Delta V Plus; Thermo) dedicated for measurements of C & N isotopes in a variety of geological solid samples. Results were calibrated against each other using different preparatory systems such as on-line combustion of organic matter in Elemental Analyzer (EA) coupled with IRMS in a continuous mode and off-line preparation of CO2 gas samples and analyzing them on standard dual-inlet system. We also present short and long term variability data of an in-house laboratory standard developed for routine C and N isotope analyses of various types of geological samples containing organic matter in order to assess stabilities/ reproducibility of the IRMS in different time windows.