Resolving isobaric interferences in direct infusion tandem mass spectrometry

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Metabolomics

Background:

• Co-fragmentation of precursors in direct infusion tandem high-resolution mass spectrometry (DI-HRMS) complicates fragment spectra.
• This spectral complexity can lead to false positives during compound identification.

Purpose of the Study:

• To introduce and validate a novel method, IQAROS (incremental quadrupole acquisition to resolve overlapping spectra), for improving compound identification in DI-HRMS.
• To address the challenge of spectral interference caused by co-fragmenting isobaric compounds.

Main Methods:

• IQAROS modulates precursor and fragment intensities by stepwise movement of the quadrupole isolation window.
• Modulated signals are deconvoluted using a linear regression model to reconstruct cleaner fragment spectra.
• Demonstrated on an Orbitrap mass analyzer with electrospray ionization (ESI) or secondary electrospray ionization (SESI).

Main Results:

• Reconstructed spectra using IQAROS accurately matched pure standards, outperforming the classical approach.
• IQAROS enabled more correct compound identifications compared to conventional methods.
• Successfully identified two isobaric biomarkers directly from a breath sample using SESI-HRMS.

Conclusions:

• IQAROS effectively generates cleaner fragment spectra for co-fragmenting isobars in DI-HRMS analysis.
• The method is user-friendly, configurable via standard instrument graphical interfaces.
• Facilitates compound characterization in DI-HRMS, particularly for high-throughput and real-time metabolomics.