Measurement of δ18O in water vapor using a tunable diode laser-based spectrometer

A gas detection system based on tunable diode laser absorption spectroscopy (TDLAS) was reported, which can be used for real-time, continuity, high-precision, and rapid time response measurement of the isotope ratio of 18 O/ 16 O in water vapor from 3729.8 cm −1 to 3730.8 cm −1 . A detailed description of the system's implementation was provided and preliminary measurement precision was analyzed with a short path length sample cell (20.4 cm) after verification in the laboratory environment. Allan variance analytical method was used to evaluate the reliability of the developed laser spectroscopic isotope analysis system and the results showed that a precision of 5.274‰ was obtained for 18 O/ 16 O ratio at 1 s signal averaging time, which can be improved to 0.088‰ at the integration time of approximate 191 s. By combining with a long optical path absorption cell, the developed TDLAS isotope detection system provides great potential for determining the oxygen isotope composition of water vapor for various applications in environmental, geological, ecological, and energy fields.