Simultaneous Mass Spectrometry and Fourier Transform Infrared Spectrometry of Off-Gases from a Thermogravimetric Analyzer

Importance of the Topic

The combined use of thermogravimetric analysis with mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR) provides comprehensive, real-time identification of gases evolved during thermal decomposition. This approach enhances material characterization, supports quality control, and advances research into polymer degradation, cement drying, and hydrate transformations.

Objectives and Overview of the Study

This work demonstrates a straightforward modification enabling simultaneous coupling of a MS and a FTIR to a TA Instruments Q5000 IR thermogravimetric analyzer (TGA). Key aims include:

• Preventing gas dilution by using a parallel heated interface.
• Achieving synchronized data collection across TGA, MS, and FTIR.
• Illustrating complementarity between the higher sensitivity of MS and the spectral clarity of FTIR.

Methodology and Used Instrumentation

The experimental setup consisted of:

• A TA Instruments Q5000 IR TGA equipped with a modified stainless-steel heated interface (200 °C).
  
• A Pfeiffer ThermoStar mass spectrometer operating in fast‐scan mode (0.2 s dwell time) across user‐defined mass ranges.
  
• A ThermoNicolet 6700 FTIR spectrometer acquiring spectra every 6 s over 400–4000 cm⁻¹ at 0.964 cm⁻¹ resolution.

Samples of calcium oxalate monohydrate, Duco® cement, and polystyrene were run in platinum pans under isothermal or dynamic heating (20 °C/min). Off‐gas flows were split: a capillary feeds MS, and the remaining gas passes through a Swagelok port to FTIR.

Main Results and Discussion

1. Calcium Oxalate Monohydrate:

• TGA displayed three distinct weight losses corresponding to H₂O, CO, and CO₂ release.
• MS trend scans confirmed m/e 18, 28, and 44 peaks; FTIR Gram–Schmidt plots yielded characteristic spectra for each gas.

2. Duco® Cement Drying:

• Isothermal TGA weight loss at room temperature indicated solvent evaporation.
• MS spectra were complicated by variable air background, while FTIR cleanly matched acetone library spectra.

3. Polystyrene Decomposition:

• TGA showed a single-step mass loss near 350 °C.
• MS data matched styrene monomer precisely.
• FTIR revealed additional oligomeric fragments in the 2800–3000 cm⁻¹ region, underscoring the complementary strengths of both detectors.

Benefits and Practical Applications

The TGA-MS-FTIR configuration offers:

• Real‐time, multispectral identification of evolved gases.
• Enhanced sensitivity for trace components (MS) alongside detailed functional group analysis (FTIR).
• Reduced sample preparation and faster analysis compared to separate runs.

Ideal applications span polymer degradation studies, cement curing monitoring, hydrate decomposition, and industrial QA/QC.

Future Trends and Potential Applications

Emerging developments include:

• Miniaturized, low‐dead‐volume interfaces to improve signal fidelity.
• Advanced software for automated library matching and chemometric deconvolution.
• Integration with gas chromatography or pyrolysis units for multi‐dimensional analysis.
• Applications in battery material aging, biomass conversion, and environmental pollutant profiling.

Conclusion

The parallel coupling of MS and FTIR to a TGA via a simple heated interface affords a robust, complementary method for evolved gas analysis. This hyphenated approach delivers high sensitivity and detailed spectral information in one simultaneous experiment, streamlining workflows and expanding analytical capabilities.

References

1. S.B. Warrington, in Thermal Analysis – Techniques and Applications, E.L. Charsley and S.B. Warrington (eds.), 1992, pp. 84–107.
2. K.G.H. Raemaekers and J.C.J. Bart, Thermochimica Acta, 1997, 295, 1–58.
3. S.B. Warrington, in Principles of Thermal Analysis and Calorimetry, P.J. Haines (ed.), 2002, pp. 174–180.