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 60 °C in a drying oven overnight.  The SIF does not accept geological carbonate samples.  Apatite is weighed at 1 mg (biogenic carbonate at 0.1 mg) into 4.5-mL Labco Exetainer vials and capped. Vials are loaded into an autosampler rack held at 30 °C and flush/filled with helium at 100 ml/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 24 h at 30 °C. 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 values of the sample peak. Final delta values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct ¹³C and ¹⁸O delta 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, 0.2 ‰