Determination of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water by means of tunable diode laser spectroscopy at 1.39 microm.
We demonstrate the feasibility of the accurate and simultaneous measurement of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water vapor by means of tunable diode laser spectroscopy. The absorptions are due to the v1 + v3 combination band, observed using a room temperature, distributed feedback (DFB) diode laser at 1.39 microm. The precision of the instrument is approximately 3, 1, and 0.5/1000 for the 2H, 17O, and 18O isotope ratios, respectively, and is at present limited by residual optical feedback to the laser. The signal-to-noise, however, is superior to that obtained in a similar experiment using a color center laser at 2.7 microm. Replacing the current laser with a better unit, we are confident that a precision well below 1/1000 is attainable for all three isotope ratios. The diode laser apparatus is ideally suited for applications demanding a reliable, cheap, and/or portable instrument, such as the biomedical doubly labeled water method and atmospheric sensing.
D003903:Deuterium / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis*; D013053:Spectrophotometry / Q000295:instrumentation* / Q000379:methods*; D014867:Water / Q000032:analysis / Q000737:chemistry*
D010103:Oxygen Isotopes; D014867:Water; D003903:Deuterium