Screening and Qualitative Identification of Antioxidant Polymer Additives by HPLC with UV/VIS and APCI-MS Detection

Importance of the Topic

Plastic and polymer materials rely on a variety of antioxidant additives to preserve mechanical and visual properties during processing and in service. These additives protect polymers against thermal, oxidative and UV degradation, extending product lifetime and reliability. Rapid screening and qualitative identification of such antioxidants is essential to ensure formulation quality, to monitor degradation pathways and to support regulatory and quality-control requirements in industries ranging from automotive components to biomedical devices.

Objectives and Study Overview

This work aims to demonstrate a combined high-performance liquid chromatography (HPLC) method with diode-array (UV/VIS) detection and atmospheric pressure chemical ionization mass spectrometry (APCI-MS) for the profiling, identification and degradation assessment of common polymer antioxidants. The study evaluates different gradient systems (methanol/tetrahydrofuran, methanol, acetonitrile) to optimize chromatographic resolution, UV baseline stability and MS response. Known standards and degraded samples are used to illustrate qualitative identification workflows and to assign structures to unknown mixture components.

Methodology and Instrumentation

Agilent 1100 series HPLC platform was configured with:

• Quaternary and binary gradient pumps with low-volume degassers
• Thermostatted column compartment (4.6×50 mm, C8, 3.5 µm)
• Diode-array UV/VIS detector (200–400 nm spectral scan, single wavelengths at 210/280 nm)
• Single-quadrupole MS with APCI interface (vaporizer 400 °C, fragmentor 100 V, nebulizer 50 psi N₂)

Gradient elution programs varied in organic solvent (acetonitrile, methanol, THF) and column temperature (30–50 °C) to assess effects on retention, UV transparency and ionization efficiency.

Main Results and Discussion

All three gradient systems provided baseline separation of low-molecular-weight phenolic antioxidants (BHA, BHQ, BHT) within 6–9 min. Resolution of larger hindered phenol oligomers (Irganox 1010, Irganox 565) and phosphite antioxidants (Naugard P, Irgafos 168) was reduced in late elution (10–12 min) under MeOH/THF and MeOH gradients, but APCI-MS enabled unambiguous identification via characteristic [M+H]+ or [M–H]– ions and fragment ions.

UV spectra were strongly influenced by mobile-phase background absorbance at low wavelengths. Acetonitrile provided the most stable baseline down to 200 nm, but reduced ionization efficiency in positive-ion MS. Methanol/THF mixtures offered balance between UV transparency and MS response.

MS fragmentation patterns varied with solvent and fragmentor voltage. For example, Irgafos 168 displayed clear [M+H]+ at m/z 647 and [M–H]– at m/z 646 in MeOH/THF, while ACN suppressed ion yield. Reduced fragmentor voltage (25 V) diminished overall ion intensity but preserved key diagnostic fragments (e.g. tert-butyl losses in Irganox 1010 at m/z 291).

Unknown real-world polymer additive extracts were matched to Naugard P analogs. Positive-ion APCI profiles of Unknown 1 and Unknown 2 revealed primary ions at m/z 689 and m/z 647, respectively. Negative-ion fragmentation supported structural assignments of differing alkyl chain lengths on the phosphite core, confirming Unknown 1 as Naugard P and Unknown 2 as a shorter-chain tris(nonylphenyl) phosphite variant.

Benefits and Practical Applications

Combined UV/VIS and MS detection offers complementary selectivity: UV spectra provide rapid fingerprinting of aromatic chromophores, while MS delivers molecular weight confirmation and fragmentation-based structural clues. This integrated approach accelerates additive screening, supports QC release testing, and enables monitoring of degradation products that may impact material performance or regulatory compliance.

Future Trends and Potential Applications

Advances in high-resolution MS (e.g. Q-TOF, Orbitrap) promise deeper structural elucidation of complex additive mixtures, including polymeric and oligomeric species. Ultra-high-performance LC (UHPLC) columns with sub-2 µm particles can further improve resolution of high-molecular-weight antioxidants. Emerging ion-mobility separations and data-independent acquisition may enhance detection of trace transformation products in real-time quality-control environments.

Conclusion

This application demonstrates that HPLC coupled with diode-array UV/VIS and APCI-MS detection provides a robust platform for qualitative identification and degradation analysis of polymer antioxidant additives. Mobile-phase composition and gradient design critically influence chromatographic resolution, UV baseline, and MS sensitivity. The methodology successfully discriminates between closely related antioxidant structures and identifies unknown additives in consumer-product extracts.

References

• Woodman M. Screening and Qualitative Identification of Antioxidant Polymer Additives by HPLC with UV/VIS and APCI-MS Detection. Agilent Technologies Application Note 5988-8610EN, 2003.