On the calibration of continuous, high-precision δ18O and δ2H measurements using an off-axis integrated cavity output spectrometer
Article first published online: 13 JAN 2009
Copyright © 2009 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry
Volume 23, Issue 4, pages 530–536, 28 February 2009
How to Cite
Wang, L., Caylor, K. K. and Dragoni, D. (2009), On the calibration of continuous, high-precision δ18O and δ2H measurements using an off-axis integrated cavity output spectrometer. Rapid Commun. Mass Spectrom., 23: 530–536. doi: 10.1002/rcm.3905
- Issue published online: 13 JAN 2009
- Article first published online: 13 JAN 2009
- Manuscript Revised: 4 DEC 2008
- Manuscript Accepted: 4 DEC 2008
- Manuscript Received: 7 OCT 2008
- Startup Grant from Princeton University
- The Office of Science (BER), US Department of Energy. Grant Number: DE-FG02-07ER64371
The 18O and 2H of water vapor serve as powerful tracers of hydrological processes. The typical method for determining water vapor δ18O and δ2H involves cryogenic trapping and isotope ratio mass spectrometry. Even with recent technical advances, these methods cannot resolve vapor composition at high temporal resolutions. In recent years, a few groups have developed continuous laser absorption spectroscopy (LAS) approaches for measuring δ18O and δ2H which achieve accuracy levels similar to those of lab-based mass spectrometry methods. Unfortunately, most LAS systems need cryogenic cooling and constant calibration to a reference gas, and have substantial power requirements, making them unsuitable for long-term field deployment at remote field sites. A new method called Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) has been developed which requires extremely low-energy consumption and neither reference gas nor cryogenic cooling. In this report, we develop a relatively simple pumping system coupled to a dew point generator to calibrate an ICOS-based instrument (Los Gatos Research Water Vapor Isotope Analyzer (WVIA) DLT-100) under various pressures using liquid water with known isotopic signatures. Results show that the WVIA can be successfully calibrated using this customized system for different pressure settings, which ensure that this instrument can be combined with other gas-sampling systems. The precisions of this instrument and the associated calibration method can reach ∼0.08‰ for δ18O and ∼0.4‰ for δ2H. Compared with conventional mass spectrometry and other LAS-based methods, the OA-ICOS technique provides a promising alternative tool for continuous water vapor isotopic measurements in field deployments. Copyright © 2009 John Wiley & Sons, Ltd.