Exploring the Potential of Electrospray-Orbitrap for Stable Isotope Analysis Using Nitrate as a Model

Area of Science:

• Analytical Chemistry
• Geochemistry
• Environmental Science

Background:

• Conventional isotope ratio mass spectrometry (IRMS) has limitations in measuring structural isotopic information for metabolites and small polyatomic ions.
• A novel approach using electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap MS) enables the measurement of multidimensional isotope signatures in intact polar compounds.

Purpose of the Study:

• To establish performance metrics for ESI-Orbitrap MS in measuring nitrate isotopologs at natural abundance levels.
• To compare the new method with conventional IRMS for isotope ratio determination.
• To develop a framework for converting isotopolog intensities to delta (δ) values.

Main Methods:

• Utilized electrospray ionization Orbitrap mass spectrometry to quantify seven nitrate isotopologs.
• Developed a framework for converting isotopolog intensities to δ values (δ¹⁵N, δ¹⁸O, δ¹⁷O).
• Applied automation and adapted measurement principles specific to isotope ratio analysis.

Main Results:

• Achieved long-term precision of 0.4‰ or better for nitrate δ¹⁵N_AIR, δ¹⁸O_VSMOW, and δ¹⁷O_VSMOW.
• Demonstrated the capability to measure non-mass-dependent oxygen isotope variations and potential clumping effects in nitrate.
• Successfully analyzed purified and unpurified environmental nitrate samples.

Conclusions:

• The ESI-Orbitrap MS method offers a robust alternative to conventional IRMS for precise isotope ratio measurements.
• This technique bridges bioanalytical MS and isotope ratio MS, opening avenues for analyzing novel isotopic signatures.
• The approach is applicable to diverse organic and inorganic solutes in various sample types.