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- Title
Automated calibration of laser spectrometer measurements of δ<sup>18</sup>O and δ<sup>2</sup>H values in water vapour using a Dew Point Generator.
- Authors
Munksgaard, Niels C.; Cheesman, Alexander W.; Gray‐Spence, Andrew; Cernusak, Lucas A.; Bird, Michael I.
- Abstract
Rationale: Continuous measurement of stable O and H isotope compositions in water vapour requires automated calibration for remote field deployments. We developed a new low‐cost device for calibration of both water vapour mole fraction and isotope composition. Methods: We coupled a commercially available dew point generator (DPG) to a laser spectrometer and developed hardware for water and air handling along with software for automated operation and data processing. We characterised isotopic fractionation in the DPG, conducted a field test and assessed the influence of critical parameters on the performance of the device. Results: An analysis time of 1 hour was sufficient to achieve memory‐free analysis of two water vapour standards and the δ18O and δ2H values were found to be independent of water vapour concentration over a range of ≈20,000–33,000 ppm. The reproducibility of the standard vapours over a 10‐day period was better than 0.14 ‰ and 0.75 ‰ for δ18O and δ2H values, respectively (1 σ, n = 11) prior to drift correction and calibration. The analytical accuracy was confirmed by the analysis of a third independent vapour standard. The DPG distillation process requires that isotope calibration takes account of DPG temperature, analysis time, injected water volume and air flow rate. Conclusions: The automated calibration system provides high accuracy and precision and is a robust, cost‐effective option for long‐term field measurements of water vapour isotopes. The necessary modifications to the DPG are minor and easily reversible.
- Subjects
WATER supply; DEW point; HUMIDITY; HYDROGEN isotopes; AIR flow
- Publication
Rapid Communications in Mass Spectrometry: RCM, 2018, Vol 32, Issue 12, p1008
- ISSN
0951-4198
- Publication type
Article
- DOI
10.1002/rcm.8131