Method development for stable isotope ratio analysis in nitrate using electrospray ionization Orbitrap mass spectrometry

english

Electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap MS) is a complementary technique to conventional isotope ratio mass spectrometry (IRMS) for the analysis of stable isotope ratios. ESI-Orbitrap MS enables the analysis of polar analytes without any prior derivatization or conversion, the characterization of molecular ions to obtain position-specific isotopologues information, high mass resolution measurements minimizing interferences, and simultaneous multielement detection. While ESI-Orbitrap MS has already been applied to isotope ratio analysis of organic and inorganic compounds, including acetate, amino acids and oxyanions, our work employs a different Orbitrap model with a specific focus on in-depth method development. This study extended isotope ratio analysis to an Orbitrap ExplorisTM 120 system using nitrate as a model compound to evaluate the capabilities and assess the performance of the chosen instrument. Many factors were considered and examined across both short and long-term measurements that may influence the accuracy and precision of delta 15N, delta 17O, and delta 18O values in nitrate, such as solvent of the sample solutions, sample introduction workflows, ESI source conditions, Orbitrap mass scan parameters and signal processing methodologies. The applicability of the development method was demonstrated on aerosol samples collected from Antarctica and the Alpine region of Northern Italy.