Premium
Automated calibration of laser spectrometer measurements of δ 18 O and δ 2 H values in water vapour using a Dew Point Generator
Author(s) -
Munksgaard Niels C.,
Cheesman Alexander W.,
GraySpence Andrew,
Cernusak Lucas A.,
Bird Michael I.
Publication year - 2018
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8131
Subject(s) - chemistry , calibration , dew point , analytical chemistry (journal) , water vapor , reproducibility , spectrometer , vapours , chromatography , meteorology , optics , statistics , physics , organic chemistry , neuroscience , biology , mathematics
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 δ 18 O and δ 2 H 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 δ 18 O and δ 2 H 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.