Identification 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

Importance of the Topic

Monoclonal antibodies (mAbs) are prone to oxidation during manufacturing, storage and formulation, which can alter their stability, efficacy and safety. Mapping oxidation sites at the peptide level is essential for understanding degradation pathways, ensuring product quality and guiding process optimization in biopharmaceutical development.

Objectives and Study Overview

This study demonstrates a workflow for identifying oxidative modifications on a model mAb by simulating stress with hydrogen peroxide. The goals were to measure changes in intact mass, pinpoint individual oxidation sites at methionine and tryptophan residues and validate assignments using high‐resolution mass spectrometry and dedicated bioinformatics tools.

Methodology and Instrumentation

Sample Preparation and Oxidation

• A purified IgG sample was weakened by treatment with 50% H₂O₂ at room temperature for 20 min to induce oxidation.
• Disulfide bonds were reduced with dithiothreitol and alkylated with iodoacetamide under denaturing conditions.
• Excess reagents were removed by dilution and the protein was digested overnight with sequencing‐grade trypsin (20:1 protein:enzyme, w/w).

Used Instrumentation

• Agilent 1260 Infinity HPLC-Chip/MS system with a nanoflow pump and integrated C18 enrichment (40 nL) and analytical (75 mm×43 µm) columns.
• Agilent 6520 Accurate-Mass Q-TOF LC/MS operated in positive mode (3 GHz, m/z 300–3200) with continuous internal mass calibration.
• Agilent MassHunter Qualitative Analysis and BioConfirm software for feature extraction, theoretical digest matching and MS/MS spectrum assignment.

Key Results and Discussion

Intact Mass Analysis

• Unmodified mAb exhibited a deconvoluted mass of 148 811.90 Da, matching the expected glycosylated form (148 811.95 Da).
• Oxidized mAb showed a broad peak at 148 950.45 Da, corresponding to an average of nine oxygen additions (~9×15.9949 Da).

Peptide Mapping and Site Localization

• Total ion chromatogram of the tryptic digest displayed sharp, well‐resolved peaks, indicating efficient chromatography on the HPLC-Chip.
• Theoretical peptide lists with mono- and di‐oxidation modifications were generated in BioConfirm and matched within ±5 ppm mass tolerance.
• Partial peptide table revealed preferential oxidation at methionine and tryptophan residues, with mass shifts of +16 Da (mono‐oxidation) or +32 Da (di‐oxidation).
• MS/MS spectra comparison of unmodified vs. oxidized peptides (e.g., NTLYLQMSSLR) showed y-ion series shifted by ~16 Da from y5 onward, confirming the specific methionine oxidation site.

Benefits and Practical Applications

This integrated LC/MS approach provides rapid, sensitive and accurate identification of oxidation sites in mAbs. It supports biopharmaceutical quality control, comparability studies, formulation screening and process monitoring by delivering detailed structural information on chemical modifications.

Future Trends and Potential Uses

Emerging directions include higher‐throughput multi‐attribute methods combining intact mass, peptide mapping and glycoanalysis in a single run; enhanced bioinformatics for automated modification profiling; and coupling with ion mobility or top-down methods for comprehensive structural characterization.

Conclusion

The combination of Agilent 1260 Infinity HPLC-Chip/MS and accurate-mass Q-TOF technology, together with dedicated software, enables precise mapping of oxidation modifications on mAbs. The workflow accelerates biopharmaceutical development by delivering high‐confidence data on degradation pathways and critical quality attributes.

Reference

1. Gudihal R. et al. Primary Characterization of a Monoclonal Antibody Using Agilent HPLC-Chip Accurate-Mass LC/MS Technology. Agilent Application Note, 2008, 5990-3445EN.
2. Gudihal R. & Waddell K. Peptide mapping of a monoclonal antibody using a microfluidic-based HPLC-Chip coupled to an Agilent Accurate-Mass Q-TOF LC/MS. Agilent Application Note, 2009, 5990-4587EN.
3. Huang L. et al. In Vivo Deamidation Characterization of Monoclonal Antibody by LC/MS/MS. Analytical Chemistry, 2005, 77(5):1432–1439.
4. Dick L. et al. Peptide mapping of therapeutic monoclonal antibodies: Improvements for increased speed and fewer artifacts. Journal of Chromatography B, 2009, 877:230–236.