Stable isotopes analyzes at LAMIR Institute 2023: standards studies

Calibration is fundamental in analytical procedures and it is carried out using reference materials, which are substances with a high level of purity and characteristics of interest with values determined with high precision. The International Atomic Energy Agency (IAEA) is an international organization that provides and regulates reference materials for laboratories around the world. The standards used in carbonate analyzes as reference for δ¹³C and δ¹⁸O (‰PDB) are: IAEA-603, that consists in calcite from a Carrara marble; NBS18 and NBS19, which were developed by the National Bureau of Standards (NBS), later renamed as the National Institute of Standards and Technology (NIST), and were produced from a marble of unknown origin and a carbonatite; IAEA -CO-9, a barium carbonate, obtained from CO₂ originated from natural gas and precipitated from a basic solution. The following standards are used as a reference for δD and δ¹⁸O (‰V-SMOW) in water analyses: the Greenland Summit Precipitation (GRESP), water from melted snow in the Summit Camp supply, in Greenland, the Standard Light Antarctic Precipitation 2 (SLAP2) prepared at the IAEA Isotopic Hydrology Laboratory in 2006 from 4 selected Antarctic snow/ice samples and the Vienna Standard Mean Ocean Water 2 (V-SMOW2) also prepared in the same laboratory in 1999 from 3 freshwater samples. LAMIR Institute provides analysis of δ¹³C and δ¹⁸O in carbonates of inorganic or organic origin and in carbonate dissolved in water. Also, it provides analysis of δD and δ¹⁸O in water. For carbonate analysis, the chemical reaction method is used with H₃PO₄ (100%) at a temperature of 72ºC, varying the reaction time depending on the sample, using a GasBench-II coupled to an IRMS Delta V advantage. For water analysis, the isotopic equilibrium method (water+H₂, for D and water+CO₂, for O) is used for both deuterium (D) and oxygen (O) using the same previous configuration. For water analyses, it is difficult to obtain certified standards, due to small production and difficult storage. That is why iLAMIR invested in the production of two internal standards (Mancini et all, 2022) iLAMIR-1A and iLAMIR-2A. To validate our results, the standards are periodically analyzed together with the samples. A compilation of all results obtained for the standards was carried out. Analyzing these results, we observed that for carbonate analyzes we have: δ¹³C ST between 0.140 and 0.093 and V between 0.015 and 0.000, δ¹⁸O ST between 0.340 and 0.175 and V between 0.464 and 0.114; for water analyzes we have: δD ST between 4.59 and 2.98 and V between 3.62 and 0.222, δ¹⁸O ST between 0.473 and 0.145 and V between 0.089 and 0.013. Therefore, we can state that the results generated by iLAMIR, for carbonate and water, are reliable and are within acceptable errors for the methodologies used.