Quadrupole Time-of-Flight Liquid Chromatograph Mass Spectrometer OAD-TOF system

Importance of the topic

Organic molecules with carbon–carbon double bonds play crucial roles in biological processes, lipid metabolism and material properties. Traditional collision-induced dissociation (CID) techniques often fail to pinpoint the exact location of these bonds. The development of oxygen attachment dissociation (OAD) enhances structural elucidation by generating radical-driven fragment ions specific to double bond positions. This capability delivers deeper insights into lipidomic research, pharmaceutical development and quality control in various industries.

Study objectives and overview

The article introduces the OAD-TOF system, a quadrupole time-of-flight liquid chromatography–mass spectrometer (Q-TOF LC–MS) integrating Shimadzu’s proprietary OAD technology. It aims to demonstrate how OAD can complement conventional CID by localizing carbon–carbon double bonds in lipids and other organic molecules. The overview details system design, operational principles and potential applications in rapid profiling and isomer separation.

Applied Instrumentation

• Shimadzu OAD-TOF system with OAD Radical Source I for radical generation via microwave discharge of water vapor and hydrogen.
• LCMS-9050 platform featuring UF-FlightTube for stable temperature-controlled flight paths and iRef TOF for enhanced energy focusing.
• LabSolutions software enabling seamless switching between CID and OAD modes.
• DPiMS QT direct probe ionization kit for minimal sample preparation workflows.
• Nexera UC supercritical fluid chromatography (SFC) system for isomer separation in lipid profiling.

Methodology

Samples containing triacylglycerols and fatty acids were analyzed by LC separation followed by MS/MS under both CID and OAD conditions. Neutral oxygen radicals generated in the radical source react selectively with double bonds, producing characteristic fragment ions. The study compared mass spectra with and without OAD to validate bond localization, achieving mass accuracy better than 3 ppm.

Key results and discussion

OAD produced distinct fragment peaks corresponding to each double bond position (n-6, n-9, n-12, n-15) in triglycerides and fatty acids. The UF-FlightTube and iRef TOF combination maintained high mass accuracy during radical fragmentation. Coupling with SFC allowed baseline separation of isomeric linolenic acids, and DPiMS QT facilitated fast triacylglycerol profiling with simple preprocessing. These results confirm OAD’s ability to reveal otherwise hidden structural details.

Benefits and practical applications

• Precise localization of double bonds in complex lipids for lipidomics and biomarker discovery.
• Enhanced structural characterization of pharmaceuticals, food components and environmental samples.
• Streamlined workflows via integrated CID/OAD switching and direct probe ionization.
• High-throughput analysis with minimal calibration drift due to optimized flight tube control.

Future trends and applications

The OAD-TOF system is poised to expand applications in metabolomics, polymer analysis and targeted isomer studies. Future developments may integrate AI-driven data interpretation, coupling with ion mobility separation and miniaturized radical sources for field-deployable platforms. OAD’s compatibility with both positive and negative ions suggests broader use in fatty acid, lipid subclass and small-molecule research.

Conclusion

By introducing neutral radical-induced fragmentation, the OAD-TOF system fills a critical gap in mass spectrometry, offering unmatched specificity for double bond localization. Its robust design, software integration and flexible ionization options make it a versatile solution for advanced analytical challenges across research and industry.