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 (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 language | English |
|---|---|
| Pages (from-to) | 25992-26008 |
| Number of pages | 17 |
| Journal | Sensors (Switzerland) |
| Volume | 15 |
| Issue number | 10 |
| Publication status | Published - 14 Oct 2015 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2015 by the authors; licensee MDPI, Basel, Switzerland.
Keywords
- Faraday effect
- Isotopic ratiometry
- Nitric oxide
- Nitrogen cycle
- Optical sensing and sensors
- Spectroscopy