title: Nitric oxide isotopic analyzer based on a compact dual-modulation Faraday rotation spectrometer.
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.
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. ejzhang@princeton.edu.
authors.forename: Eric
authors.initials: E
authors.lastname: Zhang
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. sahuang@princeton.edu.
authors.forename: Stacey
authors.initials: S
authors.lastname: Huang
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. qji@princeton.edu.
authors.forename: Qixing
authors.initials: Q
authors.lastname: Ji
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. michael.p.silvernagel.1@nd.edu.|Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. michael.p.silvernagel.1@nd.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Silvernagel
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. yin.wang@healthyphoton.com.|Now with Healthy Photon, 200 East Guoding Road, Shanghai, China. yin.wang@healthyphoton.com.
authors.forename: Yin
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. bbw@princeton.edu.
authors.forename: Bess
authors.initials: B
authors.lastname: Ward
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. sigman@princeton.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sigman
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. gwysocki@princeton.edu.
authors.forename: Gerard
authors.initials: G
authors.lastname: Wysocki
keywords: Faraday effect; isotopic ratiometry; nitric oxide; nitrogen cycle; optical sensing and sensors; spectroscopy