Nitric Oxide Isotopic Analyzer Based on a Compact Dual-Modulation Faraday Rotation Spectrometer

作者：Zhang Eric; Huang Stacey; Ji Qixing; Silvernagel Michael; Wang Yin; Ward Bess; Sigman Daniel; Wysocki Gerard^*

来源：Sensors (Switzerland), 2015, 15(10): 25992-26008.

DOI：10.3390/s151025992

• Faraday effect
• optical sensing and sensors
• spectroscopy
• nitrogen cycle
• nitric oxide
• isotopic ratiometry

We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope ((NO)-N-15) detection sensitivity of 0.36 ppbvHz(-1/2), corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 x 10(-8) radHz(-1/2) and noise-equivalent absorbance (L)(min) of 6.27 x 10(-8) Hz(-1/2). White-noise limited performance at 2.8x the shot-noise limit is observed up to similar to 1000 s, allowing reliable calibration and sample measurement within the drift-free interval of the spectrometer. Integration with wet-chemistry based on acidic vanadium(III) enables conversion of aqueous nitrate/nitrite samples to gaseous NO for total nitrogen isotope analysis. Isotopic ratiometry is accomplished via time-multiplexed measurements of two NO isotope transitions. For 5 mol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3 parts per thousand, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies.

• 出版日期2015-10