Earth and Planetary Sciences ETDs

Publication Date

Fall 10-31-2022



The simultaneous analysis of the three stable isotopes of oxygen – triple oxygen isotope analysis – has become an important analytical technique in natural sciences. Determination of the abundance of the rare 17O isotope in CO2 gas using magnetic sector isotope ratio mass spectrometry is complicated by the isobaric interference of 17O by ­13C (13C16O16O and 12C16O17O both have mass 45 amu). A number of analytical techniques have been used to measure the 17O/16O ratio of CO2 gas. They are either time consuming and technically challenging or have limited precision. A rapid and precise alternative to the available analytical methods is desirable.


We present the results of triple oxygen isotope analyses using an Aerodyne Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) CO2 analyzer configured for 16O, 17O, and 18O, combined with a custom gas inlet system. We evaluate the sensitivity of our results to a number of parameters. CO2 samples with a wide range of d18O values (from -9.28 ‰ to 39.56 ‰) were measured and compared to results using the well-established fluorination-gas source mass spectrometry method.


The TILDAS system has a precision (standard error, 2𝜎) of better than ±0.03 ‰ for d18O and ±10 per meg for Δ’17O values, equivalent to the precision of previous analytical methods. Samples as small as 3 micromoles CO2 (equivalent to 300 micrograms CaCO3) can be analyzed with a total analysis time of ~30 minutes.


We have successfully developed an analytical technique for the simultaneous determination of the d17O and d18O values of CO2 gas. The precision is equal to or better than existing techniques with no additional chemical treatments required. Analysis time is rapid and the system is easily automated so that large numbers of samples can be analyzed with minimal effort.

Degree Name

Earth and Planetary Sciences

Level of Degree


Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Zachary Sharp

Second Committee Member

Viorel Atudorei

Third Committee Member

Tyler Mackey




triple oxygen isotope, TILDAS, laser spectroscopy

Document Type