Analysis of photo polymerization initiator in UV light curingadhesives by GC/TOFMS

Importance of the Topic

The rapid, precise analysis of photopolymerization initiators in UV curing adhesives is critical for ensuring product performance, safety, and regulatory compliance. Accurate identification and characterization of residual initiators support process optimization, quality control, and environmental monitoring in industries such as electronics, coatings, and medical devices.

Objectives and Study Overview

This study aimed to detect and characterize the photopolymerization initiator remaining in a UV light curing adhesive. Using gas chromatography coupled with time-of-flight mass spectrometry (GC/TOFMS) under both electron ionization (EI) and field ionization (FI) modes, the work focused on accurate mass measurements to propose elemental compositions and deduce molecular structures.

Methodology and Used Instrumentation

The adhesive sample was analyzed on an Agilent 6890N GC with a ZB-5ms column (30 m × 0.25 mm, 0.25 µm). The temperature program started at 40 °C (1 min), ramped at 10 °C/min to 280 °C (5 min). Injection at 280 °C used split (50:1) for EI+ and splitless for FI+, with 1.0 µL volume. Helium at 1.0 mL/min served as carrier gas. Mass spectra were acquired on a JEOL JMS-T100GC “AccuTOF GC” in EI+ (70 V, 300 µA) and FI+ (-10 kV, 0 mA) over m/z 35–500 with 0.6 s scan intervals.

Main Results and Discussion

Both EI+ and FI+ total ion chromatograms showed multiple components; the unreacted initiator eluted at 27.9 min. In EI+, fragment ions at m/z 119, 147, and 201 were selected for elemental composition analysis. Unique formulas were assigned to m/z 119 (C9H11) and 147 (C10H11O), while m/z 201 was confirmed as C12H10OP based on mass accuracy, element presence, and a half-integer unsaturation indicating a fragment.

In FI+, ions at m/z 147 and 201 matched EI+ fragments, and a molecular ion at m/z 348 was evaluated. Four candidate formulas were within ±5 mDa, but C22H21O2P was chosen due to matching mass difference and plausible phosphorus/oxygen content. An integer unsaturation of 14 suggested multiple aromatic rings, leading to the proposed structure featuring phosphoric ester linked to benzene moieties.

Benefits and Practical Applications

• High mass accuracy in both EI and FI modes enables confident elemental composition assignments.
• Rapid structure elucidation aids quality assurance in adhesive production.
• Method supports detection of trace initiator residues, improving product safety.

Future Trends and Possibilities

Advancements may include coupling with soft ionization methods for intact molecular ions of larger additives, integration with automated data processing for high-throughput QA/QC, and application to complex polymer blends. Emerging TOFMS technologies could further improve resolution and sensitivity for trace-level analysis.

Conclusion

This study demonstrates that GC/TOFMS with EI and FI provides robust detection and structural characterization of photopolymerization initiators in UV curing adhesives. Accurate mass measurements enable reliable formula assignments for both fragment and molecular ions, facilitating process control and product development.

References

JEOL Ltd. Application Note No. 040 & No. 108. Analysis of photo polymerization initiator in UV light curing adhesives by GC/TOFMS. JEOL MS Data Sheet. 2007.