Analysis of Apatite/Carbonate by GasBench-IRMS
The SIF provides δ13C and/or δ18O analysis of powdered apatite and biogenic carbonate samples using a GasBench II system interfaced to a Delta V Plus IRMS (Thermo Scientific, Bremen, Germany).
Analysis of 13C and 18O in apatite/biogenic carbonate
Powdered biogenic carbonate and apatite samples are dried at 60C in a drying oven overnight. The SIF does not accept geological carbonate samples. Apatite is weighed at 3 mg (biogenic carbonate at 0.3mg) into 12-ml Labco Exetainer vials and capped. Vials are loaded into an autosampler rack held at 70C and flush/filled with helium at 100ml/min for 10-min using a CTC PAL autosampler device. Several drops of phosphoric acid (103%) are manually injected through a septum into each vial using a syringe to liberate CO2 from carbonate, and vials are returned to the autosampler rack to equilibrate for 24h at 30C. The vial headspace is analyzed for CO2 using a ThermoFisherScientific GasBench II device with a 100 µl sample loop connected to a ThermoFisherScientific Delta V Plus gas-isotope ratio mass spectrometer. A pure CO2 reference gas is used to calculate provisional delta (δ) values of the sample peak. Final δ values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct δ13C and δ18O values for laboratory reference materials are obtained. NBS 18 (-5.01‰, -23.01‰, for δ13C and δ18O respectively), NBS 19 (1.95‰, -2.20‰), and LSVEC (-46.60‰, -26.70‰) are used to calibrate data on the VPDB scale.
Limit of Quantitation and Long-term standard deviation for 13C and 18O in carbonate by GasBench-IRMS
13C and 18O in carbonate (as CO2) : Limit of Quantitation: approx. 150 nanomoles
Long-term standard deviation: 13C, 0.1 ‰; 18O, 0.3 ‰
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UC Davis Stable Isotope Facility | Department of Plant Sciences
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