Identification of Double Bond Position in Cyclic Ester using OAD TOF system

Significance of the topic

Aromatic lactones are widely used as key aroma ingredients in perfumes, detergents, and foods. The precise location of carbon–carbon double bonds within these cyclic esters strongly influences their sensory attributes and biological behavior. Conventional collision‐induced dissociation often fails to pinpoint unsaturation sites in ring structures, whereas oxygen attachment dissociation (OAD) generates radicals that selectively cleave at double bonds, offering enhanced structural resolution.

Objectives and overview of the study

This study explores a combined alkaline hydrolysis and OAD‐MS/MS approach to determine C=C double bond positions in cyclic lactones. Three representative lactones (A, A′, and B) were hydrolyzed to linear hydroxy acids and analyzed by LC–OAD‐MS/MS to assess isomer differentiation capabilities.

Methodology and instrumentation

• Sample preparation: Lactone samples (1 mmol) were dissolved in THF, treated with 1 M NaOH at 35 °C for 1 hour, extracted with hexane, evaporated, and reconstituted in IPA containing 5 mM ammonium acetate.
• Chromatography: Shimadzu Nexera X3 HPLC with a Shim-pack Scepter C18 column; gradient from 20 mM ammonium formate to ACN/IPA (1:1) at 0.3 mL/min.
• Mass spectrometry: Shimadzu LCMS-9050 in negative ion mode. CID parameters: CE 20 V; OAD radical generation (OH/O) at CE 5 V using a microwave-driven radical source introduced into Q2 cell.

Main results and discussion

• Hydrolysis converted cyclic lactones into hydroxycarboxylic acids, enabling radical‐driven OAD cleavage at unsaturation sites.
• Lactones A and A′ (C16H28O2) yielded three distinct OAD‐MS/MS fragment sets, corresponding to double bonds at positions 10, 12, and 14, which were not resolvable by CID alone.
• Lactone B (C15H26O2) produced two isomeric species with characteristic OAD fragments allowing assignment of C=C positions, whereas its CID spectra lacked diagnostic ions.
• Extracted ion chromatograms and MS/MS patterns validated the structural assignments and demonstrated OAD’s selectivity for double bond localization in cyclic esters.

Benefits and practical applications

The integrated hydrolysis and OAD‐MS/MS workflow delivers unambiguous localization of double bonds in cyclic esters. This enhances structural analysis in flavor and fragrance quality control, supports identification of isomeric aroma compounds, and can be extended to cyclic lipidomics.

Future trends and potential applications

• Application to complex natural extracts and industrial formulations for comprehensive aroma profiling and authenticity verification.
• Automation of the hydrolysis‐OAD workflow and integration with high-throughput data processing for routine quality assurance in food and fragrance sectors.
• Expansion of OAD radical chemistries and coupling with ion mobility for advanced structural analysis of diverse cyclic biomolecules.

Conclusion

Alkaline hydrolysis combined with OAD‐MS/MS on the Shimadzu LCMS-9050 enables clear assignment of C=C double bond positions in cyclic lactones, outperforming traditional CID methods. The approach holds significant promise for analytical chemistry applications in flavor, fragrance, and lipid research.