Capillary Electrophoresis-Sodium Dodecyl Sulfate (CE-SDS)

CE-SDS is a high-resolution, automated electrophoretic technique that separates proteins by molecular weight, enabling quantitative assessment of purity, identity, and stability.

• Legacy Techniques: Traditional slab-gel SDS-PAGE, which is manual, low-throughput, and provides semi-quantitative data at best.
• Established Standard: CE-SDS automates the entire SDS-PAGE workflow within a capillary, replacing the gel slab with a polymer sieving matrix and the staining/imaging process with direct UV detection. This is now the industry standard for purity testing.
• Emerging Alternatives: While CE-SDS is state-of-the-art, advancements focus on coupling the separation to mass spectrometry (CE-MS) for direct mass identification of separated peaks, providing even greater characterization detail.

Proteins are denatured with SDS and separated in a polymer-filled capillary under high voltage, with smaller proteins migrating faster. On-column UV/PDA detection generates an electropherogram.

• Output: An electropherogram plotting UV absorbance versus migration time.
• Analysis: The software integrates the peaks and calculates the corrected peak area percentage for the main peak and all impurity peaks. The migration time is used to determine the apparent molecular weight against a sizing standard.
• Interpretation: The purity of the sample is reported as the percent main peak. For a reduced monoclonal antibody, the electropherogram should show two sharp, major peaks for the heavy and light chains, with minimal surrounding impurity peaks. Any peaks outside the main ones are classified and trended as impurities.

• QC-Ready and Compliant.
• High resolution—detects closely related species and low-level impurities.
• Automated & high-throughput—supports routine manufacturing testing.
• Low sample requirements—saves scarce material.

• Method development requires significant expertise.
• Protein interactions with capillary coatings or polymers can affect resolution.
• Non-preparative—cannot recover bands for further analysis.

• Resolution: To ensure the method can clearly separate the main product peak from its critical, closely-eluting impurities.
• Precision: To prove the method yields consistent, reliable results day-to-day and analyst-to-analyst.
• LOQ: To define the lowest level of impurity that can be confidently and accurately measured.
• Accuracy: Show linearity and spike recovery.

To ensure consistent CE-SDS results across labs and time, focus on these key areas:

Method Standardization: Reproducibility relies on robust system suitability criteria, standardized sample preparation, and consistent polymer lots.

Reference Materials: Use well-characterized standards (in-house, international, or orthogonal controls) for accurate peak identification and relative quantitation.

Lifecycle Management: Regulators expect ongoing management of these standards, including stability monitoring and bridging studies for new lots, to maintain data integrity and comparability.

• mAbs/Proteins: QC release and stability under reducing/non-reducing conditions.
• ADCs/Conjugates: Quantifies conjugated species and unconjugated impurities.
• AAVs: Confirms VP1/VP2/VP3 capsid protein ratio and purity.
• VLP Vaccines: Assesses structural protein identity and purity.