Measurement of the D/H, 18O/16O, and 17O/16O Isotope Ratios in Water by Laser Absorption Spectroscopy at 2.73 μm

• Main Authors: Tao Wu, Weidong Chen, Eric Fertein, Pascal Masselin, Xiaoming Gao, Weijun Zhang, Yingjian Wang, Johannes Koeth, Daniela Brückner, Xingdao He
• Format: Article
• Language: English
• Published: MDPI AG 2014-05-01
• Series: Sensors
• Subjects: isotope ratios; water; Kalman filtering; laser absorption spectroscopy
• Online Access: http://www.mdpi.com/1424-8220/14/5/9027

A compact isotope ratio laser spectrometry (IRLS) instrument was developed for simultaneous measurements of the D/H, 18O/16O and 17O/16O isotope ratios in water by laser absorption spectroscopy at 2.73 μm. Special attention is paid to the spectral data processing and implementation of a Kalman adaptive filtering to improve the measurement precision. Reduction of up to 3-fold in standard deviation in isotope ratio determination was obtained by the use of a Fourier filtering to remove undulation structure from spectrum baseline. Application of Kalman filtering enables isotope ratio measurement at 1 s time intervals with a precision (<1‰) better than that obtained by conventional 30 s averaging, while maintaining a fast system response. The implementation of the filter is described in detail and its effects on the accuracy and the precision of the isotope ratio measurements are investigated.