Preliminary Investigation of a Range of Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) Applications

Importance of the Topic

The ability to monitor volatile organic compounds (VOCs) in real time with high sensitivity and selectivity is critical across environmental analysis, automotive interior air quality, and consumer product testing. Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) offers direct, soft ionisation and quantitation at parts-per-trillion levels without sample preparation or chromatography.

Objectives and Overview

This application note presents preliminary investigations demonstrating the versatility of SIFT-MS for:

• Calibration of ozone precursor gases using certified mixtures.
• Assessment of vehicle interior air quality (VIAQ) under ambient conditions.
• Dynamic monitoring of fragrance release from fabric detergents.

Methodology and Instrumentation

SIFT-MS employs three selectable reagent ions (H3O+, NO+, O2+) formed by microwave discharge in moist air. Reagent ions are mass-filtered, thermalised and reacted with sample VOCs in a flow tube. Product and unreacted reagent ions are analysed by a second quadrupole, and concentrations are calculated from ion count ratios and known reaction rate constants.

Instrumentation Used

• Syft Technologies Voice 200ultra with LabSyft software.
• Syft Sampling Case T0006 for interior air sampling.
• GERSTEL MPS 2 XL-xt headspace sampling system with Maestro software.

Key Results and Discussion

1. Calibration of Ozone Precursors:

• Optimised reaction rates (k) for a subset of an NPL 30-component gas mix at 4 ppbv.
• Achieved measurement precision consistent with certified values; limits of detection in the low pptv.

2. Vehicle Interior Air Quality:

• Sampling of a parked new car interior yielded real-time ppbv levels of aldehydes, BTEX and hydrocarbons.
• Measured compounds included acetaldehyde (50 ppbv), benzene (1.8 ppbv), xylenes (17.5 ppbv) and formaldehyde (41.4 ppbv).

3. Dynamic Fragrance Release:

• Continuous monitoring of limonene and dodecanal release from a detergent-soaked fabric at 30–60 °C.
• Higher temperatures increased initial headspace concentrations and accelerated decay.
• Dodecanal exhibited slower decay than limonene, indicating longer lasting fragrance persistence.

Benefits and Practical Applications

• Rapid, simultaneous detection of diverse VOCs without chromatographic separation.
• High sensitivity (pptv range) enables trace monitoring in environmental and indoor air.
• Continuous real-time data supports dynamic process studies (e.g. fragrance release).
• Reduced analysis time and complexity through direct sampling.

Future Trends and Potential Applications

• Expansion of compound libraries and reaction rate databases for emerging VOCs.
• Integration with automated sampling systems for on-site environmental and industrial monitoring.
• Applications in health diagnostics via breath analysis and food quality control.
• Development of miniaturised, field-deployable SIFT-MS instruments.

Conclusion

SIFT-MS demonstrates exceptional flexibility for quantitative VOC analysis across multiple fields. Its soft ionisation, reagent ion switching and real-time continuous measurement capabilities allow simultaneous determination of small aldehydes, aromatics and other trace gases without pre-concentration or chromatography. Calibration via known rate constants ensures accuracy, while dynamic monitoring opens new avenues in process and exposure studies.

References

• No references provided in original document