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

Eric Zhang, Stacey Huang, Qixing Ji, Michael Silvernagel, Yin Wang, Bettie Ward, Daniel Mikhail Sigman, Gerard Wysocki

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)25992-26008
Number of pages17
JournalSensors (Switzerland)
Issue number10
StatePublished - Oct 14 2015

All Science Journal Classification (ASJC) codes

  • Analytical Chemistry
  • Information Systems
  • Instrumentation
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering
  • Biochemistry


  • Faraday effect
  • Isotopic ratiometry
  • Nitric oxide
  • Nitrogen cycle
  • Optical sensing and sensors
  • Spectroscopy


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