Antibody-drug conjugates (ADCs) are among the most promising—and analytically demanding—modalities in biopharma today. By combining large, heterogeneous antibodies with chemically labile payloads and linkers, ADCs introduce a level of structural complexity that challenges conventional analytical workflows. It also poses the challenge that the very features you need to measure are often the easiest to lose during analysis.

For development teams, this creates a critical bottleneck: how to achieve deep structural characterization without destroying fragile chemistry. Traditional collision-based MS/MS methods often fragment away the very features that matter most, including fragile payloads and labile post-translational modifications (PTMs).

This limitation creates uncertainty across key development decisions, from conjugation-site assignment to comparability and stability assessments. Electron-activated dissociation (EAD) represents a shift in how this problem can be addressed, enabling preservation of fragile chemistry while still delivering detailed structural insight.

Moving beyond the limits of conventional fragmentation

Collision-based approaches such as CID are foundational tools in biologics characterization. However, for ADCs, these methods can result in incomplete or ambiguous datasets. Payload loss during fragmentation can obscure conjugation sites, while labile modifications may be degraded.

Electron-based fragmentation methods, including ETD, ECD, and EAD, address these limitations by preserving labile structures during fragmentation.

EAD, as implemented on the SCIEX ZenoTOF systems, is designed to operate within LC-compatible timescales, with fast electron capture and tunable electron energy that can be adjusted for challenging ADC species. This enables electron-driven fragmentation to be applied in workflows that align more closely with routine peptide mapping and middle-down analysis, rather than requiring specialized or extended experimental setups.

Confident payload localization without compromise

One of the clearest impacts of EAD is in payload localization. In cysteine-linked ADCs, fragile payloads are often lost during collision-induced fragmentation, thereby forcing teams to infer conjugation sites indirectly.

EAD preserves payloads on fragment ions, enabling direct localization across heavy and light chain peptides. This capability shifts analysis from inference to direct observation, reducing ambiguity and increasing confidence in site-specific assignments.

For development teams, this can mean fewer follow-up experiments and more reliable structural data to support decision-making.

Improved visibility into labile modifications and CQAs

Accurate monitoring of critical quality attributes such as glycosylation, glycation, and deamidation is essential in ADC development. These modifications are often low in abundance and sensitive to fragmentation conditions.

EAD enables these labile PTMs to be preserved and localized with confidence through the generation of diagnostic fragment ions, even at low abundance levels. This enhanced visibility supports more robust comparability and stability assessments and reduces the risk of mischaracterizing key molecular features.

Stronger confidence in disulfide mapping

Disulfide connectivity is critical for the structural integrity of cysteine-linked ADCs, yet it remains difficult to characterize using conventional methods. Limited fragmentation of disulfide-linked peptides can lead to ambiguous assignments and increased analytical burden.

EAD enables efficient cleavage of disulfide bonds while maintaining rich sequence information, supporting more confident identification of intra- and interchain linkages. This strengthens the analytical evidence base for both development and manufacturing control strategies.

Revealing subtle variants and structural liabilities

Some of the most critical variants, such as isomeric forms like Asp versus isoAsp, remain difficult to resolve with traditional MS/MS methods.

EAD provides access to diagnostic fragment ions that enable these subtle differences to be confidently distinguished, improving understanding of degradation pathways and structural liabilities.

By revealing these “hard-to-see” features earlier, development teams can make more informed decisions around formulation, storage, and product quality.

From analytical depth to workflow impact

Beyond molecular characterization, the practical value of EAD lies in its integration into routine workflows. On the ZenoTOF systems, EAD supports single-injection approaches that span multiple levels of analysis, reducing the need for multiple assays or platforms.

This can help streamline method development, reduce sample consumption, and simplify the transition from R&D to routine characterization, factors that are increasingly important as ADC pipelines scale.

A clearer path forward for ADC characterization

As conjugated therapeutics continue to evolve, the need for analytical approaches that balance depth, confidence, and efficiency is becoming more urgent.

Technologies like EAD represent an important step forward by enabling confident payload localization, accurate CQA characterization, and deeper structural insight within a streamlined LC-MS workflow on the ZenoTOF systems, so development teams can move forward with greater clarity and confidence.

Learn more about SCIEX analytical solutions for ADC development:

ADC complexity blog

ADC solution brochure

Haichuan Separation Science webinar

ADC analysis application page

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