Advances in proton transfer reaction mass spectrometry-assisted breath analysis for disease diagnosis

Proton transfer reaction mass spectrometry (PTR-MS) has emerged as a transformative tool in breath analysis, enabling real-time, high-sensitivity profiling of volatile organic compounds down to the pptv level without sample preparation. This review critically examines the technological evolution of PTR-MS, from fundamental ion-molecule kinetics to advanced configurations, including time-of-flight analyzers and switchable reagent ion technologies. We systematically evaluate the clinical potential of PTR-MS for identifying volatile signatures associated with pulmonary malignancies, infectious diseases, and systemic metabolic disorders. Despite these advances, the transition of PTR-MS from exploratory studies to routine clinical application remains limited by three major challenges: insufficient metrological traceability in quantification, qualitative ambiguity arising from isomeric overlap, and poor inter-study comparability caused by non-standardized sampling workflows. To bridge this trust gap, we propose a validation framework centered on traceable calibration, standardized breath sampling, and confidence-ranked qualitative confirmation. In particular, we advocate the use of matrix-matched reference materials for absolute quantification and the development of a standardized PTR-MS spectral atlas integrating GC retention information and reagent-ion-dependent fragmentation behavior. Such a metrological and harmonization-oriented strategy is essential for improving reproducibility, cross-platform comparability, and the clinical translation of PTR-MS in precision medicine.