Carbonate instrument method

Compilation of 101 replicate carbonate-iRMS measurements of bone hydroxyapatite from 16 stable isotope laborotories by Pestle et al. (2014). UCSC SiL measured 8 replicates shown in blue on this plot (some points are equivalent).

Kiel IV autocarbonate device with MAT 253 isotope ratio mass spectrometer

Most carbonate isotope ratio measurements at UCSC SiL are performed with a Thermo Scientific Kiel IV autocarboante device coupled to a Thermo Scientific MAT 253 isotope ratio mass spectrometer (Kiel IV-MAT 253).

The day before Kiel IV-MAT 253 analysis, your samples will be loaded into analysis vials and conditioned in a 70 °C vacuum oven overnight. In the Kiel IV autocarbonate device, individual sample vials with 10-100 microg CaCO₃ sample are converted to CO₂ gas under vacuum by drops of phosphoric acid. The CO₂ gas is cryogenically distilled from other volatiles and concentrated into a microvolume. Carbonate isotope ratios (δ¹³C_CO3 and δ¹⁸O_CO3 VPDB) of this CO₂ are measured in the MAT 253 isotope ratio mass spectrometer (iRMS) using a dual inlet for high precision analysis.

Performance of carbonate isotope ratio analysis with a Kiel IV-MAT 253 is maintained at manufacturer specification or better (Thermo Scientific specifies reproducibility of 0.05 ‰ for δ¹³C_CO3 and 0.10 ‰ for δ¹⁸O_CO3). UCSC SiL carbonate isotope ratio measurements have excellent external accuracy in the measurement of real world materials as demonstrated by the blue plot of data from Pestle et al. (2014) shown on this page.

For specialized projects, UCSC SiL is also home to a Fisons Prism III iRMS and a Thermo Scientific Gas Bench II coupled to a Delta XP iRMS.

Are you preparing a Methods section for a manuscript for samples measured with the Kiel IV-MAT 253? Here is an appropriately detailed instrument methods description that you may use for this purpose:

[Your samples] were analyzed by the UC Santa Cruz Stable Isotope Laboratory for δ¹³C_CO3 and δ¹⁸O_CO3 by acid digestion using an individual vial acid drop Themo Scientific Kiel IV carbonate device interfaced to Thermo Scientific MAT 253 dual-inlet isotope ratio mass spectrometer (iRMS). Samples are loaded into individual vials and dried overnight in a 70°C vacuum oven. During analysis, samples react at 75°C in orthophosphoric acid (specific gravity = 1.92 g/cm^3) to generate carbon dioxide and water. Water is cryogenically separated and non-condensible gases are pumped away prior to introduction of the CO2 analyte into the iRMS. All samples are measured with with several replicates of the externally calibrated Carrera Marble in-house standard reference material 'CM12' and the NBS-18 limestone international standard reference material. Samples with natural abundance carbonate isotope ratios are corrected to VPDB for offset and linearity in a two-point correction with CM12 and NBS-18. Samples with carbonate isotope ratios outside the range of natural abundance are corrected to VPDB only for offset in a single-point correction with either CM12 or NBS-18. Two natural samples of 'Atlantis II' powdered coral are run daily as independent quality control to monitor performance. Typical reproducibility of replicate measurements is significantly better than 0.05 ‰ for δ¹³C_CO3 and significantly better than 0.10 ‰ for δ¹⁸O_CO3.