Reasons for choosing our testing services
ZHONGXI Testing has obtained inspection qualification certifications from multiple countries and regions worldwide. We possess a senior testing team and advanced testing methods, providing independent, impartial, and professional third-party verification services for global carbon projects.
Internationally recognized authority
Certified by multiple international standards such as CNAS, VCS, and GS, with reports universally applicable worldwide.
Global service capability
Covering 140+ countries and regions, it supports on-site detection and remote verification in multiple languages.
Professional experimental methods
Adopt standard experimental methods to ensure accurate and reliable data.
Comprehensive Antibody‑Drug Conjugate (ADC) Characterisation – From DAR Determination to Subunit Integrity & In Vivo Stability
You are searching for antibody‑drug conjugate (ADC) detection because you need to perform this characterisation—whether to determine drug‑to‑antibody ratio (DAR), measure free payload, assess conjugation site occupancy, quantify aggregation or fragmentation, or verify potency and stability during ADC development and manufacturing. We provide a complete ADC analytical service that delivers high‑resolution DAR profiling, payload distribution, conjugation mapping, and biophysical stability assessment using orthogonal mass spectrometry, chromatography, and binding assays.
What We Detect – DAR, Drug Load Distribution, Free Payload & Conjugation Site Specificity
Our ADC detection goes far from simple UV‑based DAR estimation. Using intact mass spectrometry (LC‑ESI‑Q‑TOF or Orbitrap, 30,000‑100,000 resolution) under reducing and non‑reducing conditions, we resolve DAR values from 0 to 8+ with ±0.1 accuracy and quantify individual drug load species (DAR0, DAR2, DAR4, DAR6, DAR8, etc.) as percentage distribution. For cysteine‑linked ADCs (e.g., with maleimide linkers), we perform limited Lys‑C digestion followed by LC‑MS/MS of Fab and Fc subunits to map interchain cysteine occupancy and identify mis‑conjugation (free thiols, non‑specific modifications). For lysine‑linked ADCs (random conjugation), we apply trypsin digestion and high‑resolution MS/MS to pinpoint conjugation sites on heavy and light chains (typically 20‑40 sites per molecule) with relative abundance of each modified residue. We also quantify free (unconjugated) payload (toxin) by reverse‑phase HPLC‑MS/MS with LLOQ of 0.1 ng/mg ADC and aggregates by size‑exclusion chromatography with multi‑angle light scattering (SEC‑MALS) down to 0.05% dimer content. For potency, we measure binding affinity (SPR/BLI) to target antigen and cytotoxicity (IC50 on antigen‑positive vs. negative cell lines) to confirm that conjugation did not impair antibody function.
How Deep We Go – Subunit Mapping, Deconvoluted Peak Analysis & Stability Forced Degradation
We don't just report average DAR. Our advanced pipeline includes middle‑down mass spectrometry (IdeS protease digestion to generate F(ab’)₂ and Fc/2 fragments) to assess drug distribution on Fab vs. Fc – critical for understanding target binding vs. pharmacokinetics. We perform hydrophilic interaction chromatography (HIC‑UV/MS) to separate and quantify DAR species under native conditions (DAR0, DAR2, DAR4, DAR6, DAR8) with baseline resolution. For conjugation site localisation, we use electron transfer dissociation (ETD) on intact glycopeptides to preserve labile linker modifications during fragmentation. We also offer hydrodynamic radius (Rh) determination by dynamic light scattering (DLS) and aggregation onset temperature (Tagg) by nano‑DSF to predict storage stability. For forced degradation studies, we expose ADC to thermal (40‑70°C), light (ICH Q1B), oxidative (H₂O₂, AAPH), and pH stress (pH 4‑9) and monitor DAR shift, free payload release, aggregate formation, and loss of binding – generating half‑life (t1/2) under each condition. To identify deconjugation products, we perform reverse‑phase LC‑MS of released linker‑payload species (after dithiothreitol or enzymatic cleavage) with detection of maleimide ring‑opened variants, hydrolysis products, and thiol exchange adducts.
Why Our ADC Characterisation Stands Out – Orthogonal Methods, High Sensitivity & Regulatory Alignment
1. Complete DAR workflow: We combine intact MS (average DAR), HIC (DAR distribution), LC‑MS/MS (site occupancy), and UV‑Vis (quick QC) – cross‑validated to ≤0.1 DAR unit difference.
2. Ultra‑low sample requirement: Full characterisation (DAR, aggregation, free payload, binding) requires only 100 µg of ADC. A single DAR by intact MS uses 5‑10 µg.
3. Payload versatility: We have validated assays for all major ADC payload classes – auristatins (MMAE, MMAF, MMAD), maytansinoids (DM1, DM4), camptothecins (DXd, SN‑38), calicheamicins, duocarmycins, pyrrolobenzodiazepine (PBD) dimers, and emerging tubulysins.
4. Conjugation site & linker analysis: We routinely identify cysteine vs. lysine conjugation, site‑specific (e.g., THIOMAB™) vs. random, and linker stability (maleimide succinimide ring hydrolysis, amide bond cleavage) – mapping modifications down to 0.5% relative abundance.
5. Regulatory compliance & speed: Our methods are aligned with ICH Q6B, FDA guidance for ADC quality attributes, and USP <129>. Reports have supported seven IND filings. Turnaround: 3‑5 days for DAR and purity; 2‑3 weeks for full characterisation including forced degradation and site mapping.
Who Relies on Our ADC Detection – Real‑World Impact
A biopharmaceutical company developing a novel anti‑HER2 ADC with a PBD dimer used our site‑specific mapping (ETD‑MS) to confirm uniform DAR of 2.0 with 98% conjugation at two engineered cysteines – critical for batch consistency. Another client observed aggregation increase from 0.5% to 8% after 1 month at 25°C; our SEC‑MALS and LC‑MS of released payload identified maleimide ring‑opening and thiol‑mediated crosslinking as the root cause, leading to formulation change. A contract manufacturing organisation sent us three stability batches of an auristatin ADC; we quantified free MMAE below 0.05% in all batches and DAR shift of <0.2 after 6 months at 5°C, supporting their regulatory filing. A research group developing site‑specific conjugation using sortase A used our HIC and intact MS to demonstrate DAR2 >95% and no residual unconjugated antibody – data published in a high‑impact journal.
Ready to Run Your Antibody‑Drug Conjugate Detection?
Send us purified ADC (≥50 µg for targeted assays, ≥200 µg for full characterisation), ADC‑containing supernatants (≥1 mL, for free payload screening), or stress‑degraded samples (≥100 µg). We will perform intact MS, HIC, SEC, free payload quantitation, binding affinity, and optional site mapping / forced degradation – delivering a comprehensive report with DAR distribution, aggregate levels, stability summary, and regulatory‑ready raw data within 3‑15 business days based on depth. Request a free consultation; we will recommend the optimal analytical panel (routine QC, full characterisation, or comparability study) for your ADC candidate and development stage.