Quantitation of Oxidation Sites on a Monoclonal Antibody Using an Agilent 1260 Infinity HPLC-Chip/MS System Coupled to an Accurate-Mass 6520 Q-TOF LC/MS

Significance of the Topic

Protein oxidation, particularly methionine oxidation in monoclonal antibodies (mAbs), poses a critical challenge in biopharmaceutical development. Oxidative modifications can compromise therapeutic efficacy, alter binding properties, and impact product stability and safety. Sensitive and accurate mapping of oxidation sites supports quality control and process development, ensuring consistent product performance.

Study Objectives and Overview

The primary goal of this study was to identify and quantify oxidation sites on a monoclonal antibody using an Agilent 1260 Infinity HPLC-Chip coupled to an Accurate-Mass 6520 Q-TOF LC/MS. mAb samples were oxidized with various concentrations of t-butyl hydroperoxide (t-BHP) to simulate manufacturing-related oxidative stress. The study leveraged high-resolution mass spectrometry and dedicated data analysis software to localize oxidation events and assess their extent relative to a non-oxidized control.

Methodology and Instrumentation

Sample Preparation:

• mAb oxidation with 0–3 % t-BHP in Tris-HCl buffer at ambient temperature overnight.
• Reduction, alkylation, and trypsin digestion (20:1 protein-to-protease ratio) with quenching by formic acid.

LC/MS Analysis:

• Agilent 1260 Infinity HPLC-Chip: 5 μm ZORBAX 300SB-C18 chip, 40 nL trap, 75 mm×43 mm analytical column.
• Flow rates: 3 μL/min (capillary pump), 600 nL/min (nanoflow pump); gradient from 3 % to 95 % acetonitrile over 36 min.
• Agilent 6520 Q-TOF: positive-ion mode, m/z 300–3200, Vcap 1900 V, drying gas 5 L/min at 325 °C, fragmentor 175 V, continuous internal mass calibration.

Data Analysis:

• Agilent MassHunter Qualitative, BioConfirm, Comparative Analysis, and MassProfiler Professional software.
• Molecular Feature Extractor for peptide detection; sequence matching with preferred oxidation modifications.
• Principal Component Analysis (PCA) for sample clustering.

Main Results and Discussion

PCA clustering demonstrated clear separation of control and varying oxidation levels, confirming reproducibility. Methionine-containing peptides showed a +16 Da shift upon oxidation, with oxidized forms eluting earlier due to increased polarity. Quantitative analysis revealed:

• Met256 (DLTMISR) and Met432 (SRWQQGNVFSCSVMHEALHNHYTQK) exhibited higher oxidation susceptibility.
• Met84 (NTLYLQMSSLR) remained largely unmodified at lower t-BHP concentrations.
• Relative oxidation percentages increased proportionally with t-BHP treatment, and even control samples displayed ~1 % basal oxidation.

These findings align with reported surface exposure of Met256 and Met432 in the CH2–CH3 region, influencing oxidation risk.

Benefits and Practical Applications

The combined microfluidic HPLC-Chip and Q-TOF platform enables high-sensitivity analysis with minimal sample consumption, vital for early-stage antibody development. Automated data processing accelerates identification and quantitation of oxidative modifications, supporting process optimization, formulation screening, and quality control in biopharmaceutical workflows.

Future Trends and Applications

Emerging developments include integration of higher-throughput microfluidic systems, advanced ion mobility separations, and AI-driven data analytics for predictive oxidation profiling. Coupling orthogonal techniques, such as hydrogen–deuterium exchange or capillary electrophoresis, may further enhance structural characterization and stability assessment.

Conclusion

This study demonstrates a robust workflow for mapping and quantifying methionine oxidation in mAbs using Agilent HPLC-Chip/MS and accurate-mass Q-TOF technology. The approach delivers reliable, low-level detection of oxidative variants, facilitating critical insights during biopharmaceutical development and quality control.

Used Instrumentation

• Agilent 1260 Infinity HPLC-Chip/MS system
• Agilent 6520 Accurate-Mass Q-TOF LC/MS
• Agilent MassHunter Qualitative and BioConfirm software
• MassHunter Comparative Analysis software
• MassProfiler Professional software

References

1. Wang W, Roberts CJ. Antibody structure, instability, and formulation. J Pharm Sci. 2007;96(1):1–26.
2. Gaza-Bulseco G, Holt LJ, Fountoulakis M. Effect of methionine oxidation of a recombinant monoclonal antibody on binding affinity. J Chromatogr B. 2008;870(1):55–62.
3. Shen J, et al. Application of tert-butyl hydroperoxide oxidation to study potential methionine oxidation in recombinant antibodies. In: Marshak D, ed. Techniques in Protein Chemistry VII. Academic Press; 1996:275.
4. Chumsae C, et al. Comparison of methionine oxidation in thermally and chemically stressed samples of a fully human mAb. J Chromatogr B Anal Technol Biomed Life Sci. 2007;850:285–294.