Stable isotope laboratory

The stable isotope laboratory can provide analyses of the light isotopes13C, 15N, and 18O in a range of materials. It is equipped with a Thermo MAT 253 with Kiel IV carbonate preparation device and a Thermo Delta V Advantage with Gasbench II and Flash EA CN analyser.

Carbonates: The MAT253 is dedicated to the analysis of 18O and 13C in carbonate samples with weights in the range of 5-100 µg. The external precision (1 s) is typically 0.05‰ for 18O and 0.03‰ for 13C for samples >10µg, increasing to 0.10‰ and 0.05‰ respectively for samples ≤10µg. Large carbonate samples (100-1000 µg) are analysed on the Gasbench/Delta, with a precision of 0.08‰ and 0.06‰ for 18O and 13C respectively.

DIC: The 13C of dissolved inorganic carbon in natural waters is measured on the Gasbench/Delta via the acid-stripping method. Vials are pre-loaded with 100% phosphoric acid and flushed with helium, after which 0.5-4 ml of water is injected depending on the amount of DIC. Vials are left overnight to ensure equilibrium is reached, after which the 13C composition of the CO2 in the headspace is measured.

Water: The Gasbench/Delta is also used to analyse the 18O composition of water via equilibration with CO2. Vials are flushed with a mixture of helium with 0.3% CO2 after which 0.2 ml of water is injected. Vials are left for up to 24 hours at 25°C depending on pH to ensure equilibrium is reached, after which the 18O composition of the CO2 in the headspace is measured.

Organic matter: To measure the 13C and 15N composition of organic matter and other combustible materials the Delta is interfaced with a Flash EA Elemental Analyser. Carbon and nitrogen content of the samples can be estimated as part of the isotope analysis through calibration with known amounts of an in-house standard. The Flash EA can also be used in stand-alone mode to measure C and N content only.