Immunoaffinity-LC-MS/MS Quantification Service

A fundamental limitation of direct LC-MS-based protein quantification is dynamic range — in plasma, 95% of protein mass comes from just 12 abundant proteins, while the majority of clinically relevant biomarkers exist at low ng/mL or below. Immunoaffinity-LC-MS/MS breaks this limitation by adding a specific antibody-based enrichment step before mass spectrometric analysis, concentrating the target analyte while eliminating matrix interferences and delivering 100-1,000× sensitivity improvement over direct LC-MS. As part of our comprehensive targeted proteomics and absolute quantification portfolio, IA-LC-MS/MS bridges the gap between direct LC-MS and immunoassay-level sensitivity for low-abundance targets. We provide end-to-end support from antibody reagent selection and assay design through method development, analytical validation, and sample cohort analysis.

• Protein-Level Immunocapture: Target-specific antibodies immobilised on magnetic beads capture intact proteins from biological matrices, followed by on-bead digestion and LC-MS/MS quantification — ideal for targets with well-characterised antibodies or when PTM/isoform information must be preserved.
• Peptide-Level SISCAPA Enrichment: Anti-peptide antibodies capture specific proteotypic tryptic peptides after total sample digestion, providing a scalable workflow for multiplexed quantification of 5–30+ targets per assay with sub-ng/mL sensitivity.
• PRM/4D-PRM Readout with Stable Isotope Standards: High-resolution parallel reaction monitoring on Orbitrap and timsTOF platforms with AQUA heavy-labeled or full-length SILAC protein internal standards for absolute quantification with defined LOD, LOQ, and inter-assay reproducibility.

Understanding Immunoaffinity-LC-MS/MS: Bridging the Sensitivity Gap

The sensitivity of any LC-MS-based protein quantification method is ultimately limited by the efficiency with which target peptides can be ionised against a background of non-target peptides from co-digested matrix proteins. In direct LC-MS analysis of plasma, the total peptide background from abundant proteins creates a dense chemical noise floor that obscures low-abundance targets. Even with abundant protein depletion or fractionation, the practical LOD for direct LC-MS quantification in plasma typically falls in the low µg/mL range — insufficient for the vast majority of protein biomarkers that exist at low ng/mL or below.

Immunoaffinity enrichment breaks this limitation by physically isolating the target species from the matrix background before LC-MS analysis. The enrichment step provides two synergistic benefits: the target is concentrated 10-50× from a larger sample volume into a small elution volume, and the vast majority of matrix proteins are removed during washing, dramatically reducing chemical noise and ion suppression. The combined effect delivers the 100-1,000× sensitivity improvement that makes IA-LC-MS/MS capable of quantifying proteins at sub-ng/mL concentrations in plasma. Our Precision Quantification service hub integrates IA-LC-MS/MS as a core capability, ensuring seamless transition between direct LC-MS workflows and immunoaffinity-enhanced quantification as project sensitivity requirements change.

Dual Enrichment Strategy for Every Target Type

Different target types and project requirements demand different enrichment strategies. Protein-level immunocapture preserves conformational epitopes and PTMs, making it the preferred approach for biotherapeutic quantification where the capture antibody targets a unique structural feature. Peptide-level SISCAPA enrichment offers inherently greater multiplexing capability — multiple anti-peptide antibodies can be combined in a single digest — making it the optimal choice for biomarker panels where 5-30+ targets must be quantified simultaneously. Our team selects the appropriate enrichment strategy based on target properties, required sensitivity, and multiplexing needs, and can develop custom anti-peptide or anti-protein antibodies for novel targets.

For projects requiring both protein complex characterization and absolute quantification, our IA-LC-MS/MS workflow integrates with IP-MS Absolute Quantification — the target protein is immunoprecipitated under native conditions along with its interaction partners, and the entire complex is analysed by LC-MS/MS with AQUA internal standards for each detected subunit, providing stoichiometric quantification of protein complexes in a single workflow.

Whichever enrichment strategy is selected, the readout platform remains consistent: high-resolution parallel reaction monitoring on Orbitrap or 4D-PRM on timsTOF instruments, providing confident peptide identification through full MS/MS spectral matching even at the low signal levels characteristic of immunoaffinity-enriched samples. This combination — specific enrichment plus high-resolution MS detection — creates a quantification method that matches immunoassay sensitivity while exceeding it in specificity and multiplexing capacity.