Aggregate and Fragment Analysis - Agilent BioHPLC Columns Application Compendium

Significance of Topic

Monitoring aggregation and fragmentation in therapeutic proteins is critical to ensure product safety and efficacy. Size exclusion chromatography (SEC) is widely adopted for its ability to separate monomers from higher-order aggregates and low-molecular fragments without denaturing the protein under native conditions.

Objectives and Study Overview

This application note demonstrates method development for the NISTmAb reference monoclonal antibody. The goals were to optimize mobile phase composition and pH to achieve balanced peak symmetry, high resolution between monomer and dimer species, and accurate quantitation of high-molecular-weight (HMW) variants.

Methodology and Used Instrumentation

The study employed an Agilent 1260 Infinity II Bio-inert LC system with a quaternary pump, multisampler, bio-inert column compartment, and variable wavelength detector (DAD). An Agilent AdvanceBio SEC 200 Å, 1.9 µm, 4.6 × 300 mm column provided reduced secondary interactions. Buffer Advisor software generated mobile phases from stock solutions of NaH₂PO₄, Na₂HPO₄, and NaCl over pH 6.6–7.4.

Main Results and Discussion

At 150 mM phosphate without NaCl, pH 7.4 yielded the best compromise of dimer/monomer resolution (Rs ∼2.8), symmetry, and HMW% close to the reference value. Addition of NaCl allowed reduction of phosphate concentration: 50 mM phosphate with 250 mM NaCl at pH 6.8 delivered optimal peak shape (As ∼1.33), Rs ∼2.86, and accurate HMW quantitation. Higher salt or buffer levels reduced resolution or increased tailing.

Benefits and Practical Applications

• Rapid screening of buffer conditions using Buffer Advisor accelerates method development.
• Bio-inert SEC packing minimizes unwanted interactions with larger biomolecules.
• Optimized mobile phase (50 mM phosphate, 250 mM NaCl, pH 6.8) ensures consistent aggregate quantification.

Future Trends and Applications

Integration of SEC with multi-angle light scattering (SEC-MALS) and native mass spectrometry (SEC-MS) will further enhance characterization of subtle conformational variants. Advances in UHPLC systems and ultra-small particle columns will continue to reduce run times while maintaining resolution.

Conclusion

A systematic approach using a bio-inert LC platform and Buffer Advisor software enabled identification of a robust SEC method for NISTmAb aggregate analysis. The optimized conditions achieve reliable separation, reproducible quantitation, and can be applied to other therapeutic antibodies.

References

• Schiel JE et al. Anal Bioanal Chem. 2018;410:2127–2139.