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.

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