Modified Method for Trapping and Analyzing ¹⁵N in NO Released from Soils

Area of Science:

• Environmental Science
• Soil Science
• Isotope Geochemistry

Background:

• Investigating soil nitric oxide (NO) sources is crucial for understanding nitrogen cycling.
• Direct ¹⁵N isotope tracing of NO is challenging due to its reactivity and low soil-surface concentrations.
• Existing wet-chemical methods are often unsuitable for the low NO concentrations found in soil environments.

Purpose of the Study:

• To develop and validate a modified method for efficient trapping and conversion of low-concentration NO for ¹⁵N analysis.
• To enable accurate isotopic quantification of NO derived from various soil nitrogen pools.
• To improve the investigation of soil NO production pathways using ¹⁵N isotope tracing.

Main Methods:

• Quantitative oxidation of NO to NO₂ using chromium trioxide (CrO₃).
• Conversion of NO₂ to nitrite (NO₂^-) and nitrate (NO₃^-) in an alkaline hydrogen peroxide (H₂O₂) solution.
• Reduction of NO₂^- and NO₃^- to nitrous oxide (N₂O) using a denitrifier method for ¹⁵N analysis.

Main Results:

• Achieved NO trapping efficiencies exceeding 85% for 50 ppb NO in an air stream.
• Demonstrated high precision: 0.29‰ (δ-values) for natural abundance NO and 0.13 atom % for labeled NO.
• Successfully identified distinct ¹⁵N abundances in NO from soil amendments (¹⁵NH₄NO₃, NH₄¹⁵NO₃, Na¹⁵NO₂).

Conclusions:

• The modified method provides an effective and precise approach for ¹⁵N analysis of low-concentration soil NO.
• This technique is suitable for both natural abundance and ¹⁵N labeling studies in soil ecosystems.
• The method facilitates the elucidation of NO sources and pathways in diverse soil environments.