Degradation of rotary vacuum pump oil determined by field desorption (FD) - TOFMS and group-type analysis software

Importance of the topic

The performance and longevity of vacuum pumps are highly dependent on the condition of their lubricating oil. Monitoring chemical changes in pump oil helps prevent system failures and contamination, supporting reliable industrial and research operations.

Objectives and study overview

This study aimed to compare the molecular composition of new and used rotary vane pump oil using field desorption time-of-flight mass spectrometry (FD-TOFMS). Group-type analysis software was applied to the mass spectra to quantify variations in hydrocarbon classes and infer degradation pathways.

Methodology and instrumentation

• Sample materials: New and used rotary vane pump oil
• Ionization technique: Positive field desorption (FD+)
• Mass spectrometer: JMS-T100GC 'AccuTOF GC'
• Cathode potential: -10 kV
• Emitter current ramp: From 0 to 40 mA at 51.2 mA/min
• Mass range: m/z 35–1600
• Spectral acquisition interval: 0.5 s

Key results and discussion

FD mass spectra of both oils showed typical hydrocarbon distributions with subtle differences. Group-type analysis revealed that used oil exhibits:

• Increased fractions of saturated (CnH2n+2) and moderately unsaturated species (CnH2n, CnH2n-2)
• Decreased proportions of highly unsaturated hydrocarbons (CnH2n-4, CnH2n-6, CnH2n-8)

This suggests hydrogenation of multiple bonds, ring opening or oxidative degradation of unsaturated components. Apparent shifts in polymer distribution metrics (Mn, Mw, PD) further support progressive oil aging.

Benefits and practical applications

• Soft ionization preserves intact molecular ions, enhancing molecular-level insights
• Group-type analysis quantifies compositional shifts, enabling routine oil health monitoring
• Early detection of degradation helps schedule preventive maintenance and avoid equipment downtime

Future trends and applications

• Integration of high-resolution MS to resolve isobaric oxidation products
• Automated data analysis pipelines for real-time oil condition assessment
• Extension to diverse lubricant types and operational environments
• Linking compositional data with predictive maintenance algorithms

Conclusion

Field desorption TOFMS combined with group-type analysis effectively discriminates new and used vacuum pump oil compositions. This approach provides a powerful tool for lubricant condition monitoring and supports improved maintenance strategies in industrial and analytical settings.