Analytical services: Carbonate 未18O and 未13C isotopes
The SPA lab has two automated analyzers for biogenic and inorganic mineral carbonate 未18O and 未13C isotopes: a Kiel IV Carbonate Device and a GasBench II, both of which are coupled to the MAT-253 LGIR mass spectrometer. The Kiel device is slower and more expensive to run but has marginally better precision at small samples sizes (<50 碌g of pure carbonate). The Kiel device is limited to solid carbonate material. The Gasbench has faster throughout, uses cheaper consumables and generally is more likely to work at any given time. The Gasbench can analyze the isotopic composition of DIC as well as solid carbonates.
Solid carbonate samples are analyzed for 未18O and 未13C isotopes by acid digestion using an individual vial acid drop ThemoScientific Kiel IV carbonate device interfaced to ThermoScientific MAT-253 dual-inlet isotope ratio mass spectrometer (IRMS). Air is removed from the reaction vial using vacuum pumps. Samples are reacted at 70掳C in orthophosphoric acid (specific gravity ~ 1.90 g/cm3) to generate carbon dioxide and water. Water is cryogenically removed from CO2 and non-condensable gases are pumped away, prior to introduction of the purified CO2 into the IRMS.
During a run sequence, three each of NBS-19 and LSVEC international standards are
used to normalize isotope results using a two-point linear normalization technique.
Two NBS-19 limestone samples are run "as a sample" to monitor quality control and
long-term performance. Normalized delta values are expressed relative to VPDB for
未13C and 未18O.
Gas Bench II
Solid carbonate 未13C and 未18O ratios in carbonate minerals can be determined by the analysis of CO2 generated by the reaction of carbonate with orthophosphoric acid. Air is removed from the reaction vial by flushing with pure helium. Depending on the carbonate material, the reaction is kept at 72掳C and allowed to proceed for between 1 and 48 hours. Calcite often requires only 1 hour, aragonite requires 24 hours, while dolomite and apatite require 48 hours. The CO2 gas evolved ends up in the headspace of the reaction vial such that the 未13C of the CO2 gas is equivalent to that of the carbonate. The headspace CO2 is analyzed using a MAT-253 IRMS. The SPA lab uses smaller 4.5 ml vials (see Breitenbach and Bernasconi 2011) to successfully analyze 20 碌g of carbonate with the same precision as 100 ug in the standard 12 ml Labco vial.
During a run sequence, three each of NBS-19 and LSVEC international standards are used to normalize isotope results using a two-point linear normalization technique. Two NBS-19 limestone samples are run "as a sample" to monitor quality control and long-term performance. Normalized delta values are expressed relative to VPDB for 未13C and 未18O.
Automated 未18O and 未13C carbonate device rates
Dual Inlet: Kiel IV Carbonate Device
| Isotope | Phase | Quantity | Measurement Precision | Internal | External |
| 未18O, 未13C | Solid | 20鈥�50 碌g | 卤 0.08 鈥� | $10 | $16 |
Sample types: Biogenic and inorganic minerals (e.g., calcium carbonate, fossil calcite shells).
Conflo: GasBench II
| Isotope | Phase | Quantity | Measurement Precision | Internal |