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Sensors (Basel). 2015 Oct 14;15(10):25992-6008. doi: 10.3390/s151025992.

Nitric oxide isotopic analyzer based on a compact dual-modulation Faraday rotation spectrometer.

Author information

1
Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. ejzhang@princeton.edu.
2
Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. sahuang@princeton.edu.
3
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. qji@princeton.edu.
4
Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. michael.p.silvernagel.1@nd.edu.
5
Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. michael.p.silvernagel.1@nd.edu.
6
Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. yin.wang@healthyphoton.com.
7
Now with Healthy Photon, 200 East Guoding Road, Shanghai, China. yin.wang@healthyphoton.com.
8
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. bbw@princeton.edu.
9
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. sigman@princeton.edu.
10
Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. gwysocki@princeton.edu.

Abstract

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 ((15)NO) 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.

KEYWORDS:

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

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