Solid samples are analyzed for δ¹⁸O and δ¹³C isotopes by acid digestion using an automated common acid bath carbonate device interfaced to either a Fisons Prism III or Optima dual-inlet isotope ratio mass spectrometer (IRMS). Samples are reacted at 90°C in orthophosphoric acid (specific gravity = 1.92 g/cm³) to generate carbon dioxide and water. Water is cryogenically removed from CO₂ and non-condensible gases are pumped away, prior to intrduction of the purified CO₂ into the IRMS.

During a run sequence, calibrated in-house standard Carrera Marble is used to correct the data including a drift correction. Two NBS-19 limestone samples are run "as-a-sample" to monitor quality control and long term performance. Carrera Marble has been extensively calibrated against NIST Standard Reference Materials (NBS-19, NBS-18, and LSVEC) and as part of intercomparison studies with other stable isotope laboratories.

Corrected delta values are expressed relative to international standards PDB (PeeDee Belemnite) for δ¹³C and δ¹⁸O.

Sample Size: For pure calcium carbonate measurements sample sizes of 50-70 µg is optimal. Samples should be kept to under 200 µg and greater than 20 µg for best results. For smaller samples, contact the lab manager to discuss your circumstances. Samples as small as 5 µg have been reliably measured. For bulk sediment samples an estimate of percent inorganic carbon is useful to ensure a proper amount of sample is run.

Sample Submission:

Two Steps:

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UCSC - Earth and Planetary Sciences
Stable Isotope Laboratory
1156 High Street, E&MS C512
Santa Cruz, CA 95064
Phone: 831-459-5857