Improved precision and throughput for 17O-excess measurements on water with Cavity Ring-Down Spectroscopy

Triple oxygen isotope data (denoted as ¹⁷O-excess) have been used to constrain meteorological processes, plant fractionation processes, animal metabolism, and a variety of other physical and chemical processes. Measurement precision is key in order to successfully apply this promising new tracer to a range of scientific questions. Up to date, the highest measurement precision for ¹⁷O-excess on water was achieved by converting water to O₂ and subsequent mass spectrometric analysis of O₂ (Barkan and Luz, 2005). This approach allows to reach a measurement precision of about 5-6permeg. However, it is very difficut to setup and only a few laboratories worldwide succesfully use this methodology. A far simpler approach is to use Cavity Ring-Down Spectroscopy (CRDS), i.e. the Picarro L2140-i analyzer that measures δ¹⁸O, δ¹⁷O, δD and determines ¹⁷O-excess. To date, the ¹⁷O-excess measurement precision of CRDS was limited to 10-15permeg. Here, we will present a new metholodology that allows to reach a similar or even better precision compared to the mass spectrometric approach. The improved methodology does not require any hardware changes but is solely based on modifications of the injection procedure.