Isotope analysis of water by means of near-infrared dual-wavelength diode laser spectroscopy

A novel diode laser spectrometer was developed using dual-wavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water. A 1.4-µm diode laser probed a H16OH/HO2H line pair near 7198 cm-1, while a similar laser observed H16OH, H17OH, and H18OH ro-vibrational lines around 7183 cm-1, or a H16OH/H18OH line pair near 7200 cm–1. The 1-σ standard deviation is 0.2‰ for 18O/16O, and 0.5‰ for the 2H/1H and 17O/16O isotope ratios. Preliminary experiments with repeated injections of a natural abundance sample point to an accuracy of about 1‰ for all three isotope ratios in natural samples.