Multiple reference carbonate materials for high precision analysis of clumped isotope thermometry
Abstract
We report here long term precision of three carbonate reference materials analysed along with other inter-laboratory carbonates (ETH1, ETH3) and Heated Gas (HG). In these experiments we followed the recipe where HG of variable compositions (derived from the samples and carbonate references) were analysed routinely for assigning the Cap47 values. The process enabled getting a linearity correction based on relationship between 47 HG (Raw) [] and 47 HG (Raw) [] in the batch (comprising of 20 samples or more). The routine analytical protocol involves zero enrichment using working gas (Linde CO2) followed by analysis of carbonate reference material, samples and HG prepared from the CO2 recovered from sample after each analysis. Occasionally, we tuned our protocol analyzing equilibrated CO2 with water at different temperatures to check any drift [2] . Experiments conducted in a batch used three different carbonate references i.e. MAR J1, refer to Carara marble powder (<250 mesh), while OMC (<100 mesh) and OASIS are calcite powders obtained from Otavi Meieberg, Namibia and Eastern Ghat [1,2]. Our analytical protocol involved processing the carbonate powder using break seal method where CO2 prepared by reacting with >100% phosphoric acid for 24 hours in an external setup at 25C was further cleaned in a GC column before analysis [2]. Our experimental demand is 5 mg of powder, which yields major beam voltage of 10KV usually run for 100 cycles (in 10 acquisition), with a tolerance of 10% drop in the voltage in each acquisition. The long term mean value of 47 (CDES) and precision of repeat analysis of carbonate reference materials (mean 1SE; Number of analysis) are as follow: MARJ1 (0.3910.002; n= 62), OMC (0.5790.005, n=24), and OASIS Calcite (0.4970.005, n=9). Similarly, the long term mean value and reproducibility (1SE) for 13C (VPDB) and 18O (VPDB) are as follow: a) MARJ1 (2.060.01, n=62 and -2.020.03, n=62), b) OMC (-4.220.01, n=24 and -8.340.05, n=24), and c) OASIS Calcite (1.340.01, n=9 and -10.870.02, n=9). During our analysis, we monitored 49/44 ratio and accepted only those values where it is less than 0.1 to define the level of contamination during sample preparation following protocol of Gas Chromatography cleaning. Our analytical procedure is reproducible (with less than 10% outlier) and robust, providing best method for high precision analysis of clumped isotope in carbonate samples. References: 1. Ghosh et al., 2005. Rapid Communications in Mass Spectrometry. 19(8), pp.1097-1119. 2. Fosu et al., 2019. Rapid Communications in Mass Spectrometry. Vol. 33(2), pp.203-214.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMPP44B..07G