🧮 Rmax Calculator

⚠️ Capture-Based Methods

A low analyte Rmax doesn't always mean low mass transport risk. With capture-based methods, if your analyte is small relative to the ligand (e.g., a fragment binding an IgG), the Rmax in RU will be low — but the actual binding site density (captured ligand level) can be very high. Mass transport depends on binding site density × ka, not the observed Rmax. So 20 RU Rmax from a small analyte on a dense capture surface can still give significant transport limitation. Always assess the Damköhler number based on the captured ligand level, not just the analyte response.

🧪 Check Your Protein Before Coupling

If your observed Rmax is consistently lower than theoretical, the problem might not be your surface — it might be your protein. Aggregated samples reduce functional Rmax because you're immobilizing a mix of active monomer and inactive aggregates; the aggregates contribute mass (and response during immobilization) but no binding activity, so the observed analyte Rmax ends up lower than expected. Run SEC (size-exclusion chromatography) before coupling to verify your ligand is monomeric and active.

✅ Quick Diagnostic

Compare observed Rmax to theoretical:

• • <30% of theoretical → Ligand lost activity during immobilization, steric hindrance, surface degradation, orientation effects (e.g., random amine coupling occluding the active site), partial denaturation by coupling chemistry, or incorrect MW assumption (e.g., using monomer MW for an obligate dimer)
• • 30–80% of theoretical → Normal range for most surfaces
• • >100% of theoretical → Non-specific binding or wrong stoichiometry assumption (e.g., analyte binding multiple ligand sites, or using incorrect MW)