Analysis of butylene glycol oligomer samples by temperature-rising direct analysis in real time mass spectrometry (TR-DART-MS)

Significance of the Topic

Understanding the structural distribution and thermal behavior of butylene glycol oligomers is critical for quality control in chemical manufacturing, cosmetics, and materials science. Traditional mass spectrometry techniques require extensive sample preparation and often lack the ability to provide dynamic information under changing temperature conditions. The combination of direct analysis in real time (DART) ionization with a temperature-rising device (ionRocket) offers a rapid, minimally preparative method to monitor molecular weight distributions and detect additives or polymer degradation products in real time.

Objectives and Study Overview

This study aimed to evaluate the performance of temperature-rising DART-MS (TR-DART-MS) for two butylene glycol oligomer samples of different average molecular weights and for a common polyethylene bag material. Specific goals included:

• Comparing mass spectral profiles of oligomer samples under constant temperature DART and temperature-ramping TR-DART conditions.
• Determining differences in molecular weight distribution between sample A and sample B.
• Detecting additives and pyrolysis products in polyethylene by controlled thermal ramping.

Methodology and Instrumentation

The analytical setup integrated a DART-OS ion source with the ionRocket temperature-rising device and a Shimadzu LCMS-8030 triple quadrupole mass spectrometer.

• DART conditions: helium gas, 450 °C ion source temperature, direct sample introduction.
• IonRocket program: ramp from room temperature to 600 °C over 7 minutes.
• Mass spectrometer: polarity switching in 15 ms, scanning 50–1500 u at up to 15,000 u/s, Q1 full scan mode in positive/negative simultaneously.
• Samples: liquid butylene glycol oligomers (direct application) and solid polyethylene bag (cut to size).

Main Results and Discussion

Under constant-temperature DART, both oligomer samples showed series of peaks separated by 72 u (butylene glycol repeat units). However, TR-DART-MS provided additional insight:

• Sample A (lower average MW) displayed highest-intensity ions in the m/z 600–900 range at 4–5 minutes of the temperature ramp.
• Sample B (higher average MW) extended to m/z 500–1300, indicating a larger molecular weight distribution.
• Thermal profiling revealed shift of oligomer signals to higher m/z with increasing temperature, reflecting successive desorption and ionization of larger chains.
• Polyethylene bag analysis identified Irgafos 168 antioxidant (m/z 663 mono-oxide, m/z 736 di-oxide) at 3.7–4.5 minutes and polymer pyrolysis fragments (14 u interval) at 4–5.5 minutes.

Benefits and Practical Applications

TR-DART-MS offers several advantages for industrial and research laboratories:

• Rapid, direct analysis without chromatographic separation or complex sample prep.
• Real-time thermal profiling of oligomer distributions to assess product consistency.
• Simultaneous detection of additives and polymer degradation products in packaging materials.
• High throughput screening for QA/QC in polymer and cosmetic industries.

Future Trends and Potential Applications

Advancements in temperature-rising ambient ionization could expand to:

• Automated thermal mapping of complex mixtures in food, pharmaceutical, and environmental samples.
• Integration with high-resolution mass analyzers for exact mass determination of thermal degradation pathways.
• Coupling with chemometric tools to build predictive models of polymer aging and additive release.

Conclusion

Temperature-rising DART-MS effectively differentiates butylene glycol oligomers of varying chain lengths and detects additives and pyrolysis products in polymers with minimal sample preparation. The dynamic thermal profiling capability enhances molecular weight characterization and supports rapid quality assessments.