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Open AccessArticle

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

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Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA
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Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
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Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
4
Now with Healthy Photon, 200 East Guoding Road, Shanghai, China
*
Author to whom correspondence should be addressed.
Academic Editors: Mark A. Arnold and Hoeil Chung
Sensors 2015, 15(10), 25992-26008; https://doi.org/10.3390/s151025992
Received: 31 July 2015 / Revised: 28 September 2015 / Accepted: 8 October 2015 / Published: 14 October 2015
(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)
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 (15NO) detection sensitivity of 0.36 ppbv·Hz−1/2, corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 × 10−8 rad·Hz−1/2 and noise-equivalent absorbance (αL)min of 6.27 × 10−8 Hz−1/2. White-noise limited performance at 2.8× the shot-noise limit is observed up 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 μmol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3‰, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies. View Full-Text
Keywords: Faraday effect; optical sensing and sensors; spectroscopy; nitrogen cycle; nitric oxide; isotopic ratiometry Faraday effect; optical sensing and sensors; spectroscopy; nitrogen cycle; nitric oxide; isotopic ratiometry
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Zhang, E.; Huang, S.; Ji, Q.; Silvernagel, M.; Wang, Y.; Ward, B.; Sigman, D.; Wysocki, G. Nitric Oxide Isotopic Analyzer Based on a Compact Dual-Modulation Faraday Rotation Spectrometer. Sensors 2015, 15, 25992-26008.

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