Carbonate analysis at SIREAL is done with a ThermoElectron Gasbench II coupled to a ThermoElectron Deltaplus XP IRMS in continuous-flow mode. From this, we are able to measure δ13C and δ18O simultaneously.

The Gasbench itself is the box with the gauges in the back. The big black box on stilts is the heating block in which we place samples of bioapatite and carbonate for analysis.

Our methods

Between 200 and 2000 μg of powdered and pretreated carbonate-bearing rock is placed into a 4mL vial, capped with a pierceable septum

Vials for carbonate analysis

Vials are flushed with helium to remove any room air. Then 103% phosphoric acid is injected through the septum. The resultant reaction releases carbon dioxide into the vial. A sample needle draws this carbon dioxide out and into the ion source of the mass spectrometer.

A single analysis is the result of ten pulses of gas from the vial into the ion source. The delta values for these ten peaks are then averaged to provide the reported value and the standard deviation of the values of the ten peaks provides analytical error.


Rates are $20 per sample. There is no additional charge for replicates or standards. We only charge for successful analyses.

Packaging your samples

Samples for carbonate analysis may be send in any form, though there will be an extra $5 per sample charge if we receive solid rock and have to powder them ourselves. Pretreated or unpretreated powdered samples are best sent in carefully labeled 1.5-1.7 mL microcentrifuge vials. Make sure both the tops and the sides of the vials are labeled, as these markings are often rubbed off during pretreatment and weighing.

A typical 1.5 mL microcentrifuge vial. The blue line toward the bottom represents the ideal sample size (though with pure carbonates we can work with half that much).

Our analyses only require 200 μg of pure carbonate, but we may need to weigh as much as 2 mg for an adequate analysis. Sending us 10-20 mg of powder is ideal.

When you’re ready to send your samples

Please visit our Send Your Samples page for instructions for submitting your samples for analysis at SIREAL


If you have questions or concerns, please contact Penny Higgins at pennilyn [dot] higgins [at] rochester [dot] edu.