---
title: "How is peptide aggregation measured? Size-exclusion chromatography explained | Sable Peptides"
description: "How size-exclusion chromatography (SEC) separates monomer from dimers and higher aggregates, the role of MALS detection, artefacts from column interactions, and when SEC is relevant to peptides. Research use only."
canonical: https://www.sablepeptides.co.uk/guides/size-exclusion-chromatography-for-peptide-aggregates
dateModified: 2026-10-16
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# How is peptide aggregation measured? Size-exclusion chromatography explained

Size-exclusion chromatography (SEC) separates molecules by size as they pass through a porous column: large aggregates elute first, monomer later. Reported as percent monomer and percent high-molecular-weight species, it is the standard way to quantify soluble aggregates. Multi-angle light scattering (MALS) adds an absolute molar mass for each peak.

## How does SEC separate by size?

Small molecules enter the pores of the stationary phase and take a longer path; large ones are excluded and elute earlier. Unlike reversed-phase HPLC, SEC uses mild aqueous mobile phases intended to keep non-covalent aggregates intact. Theory and practice for aggregate analysis are reviewed in detail.

Source: [Theory and practice of size exclusion chromatography for analysis of protein aggregates, J Pharm Biomed Anal 2014 (PubMed 24816223)](https://pubmed.ncbi.nlm.nih.gov/24816223/)

## What does MALS add?

Calibrating SEC with standards assumes the sample has a similar shape. MALS measures scattered light directly to give molar mass independent of elution time, so a peak can be confirmed as a dimer or trimer rather than inferred.

Source: [Characterization of proteins by SEC-MALS, J Vis Exp 2019 (PubMed 31282880)](https://pubmed.ncbi.nlm.nih.gov/31282880/)

## How does SEC compare with other aggregate checks?

| Method | Measures | Strength | Weakness |
| --- | --- | --- | --- |
| SEC(-MALS) | Soluble aggregates by size | Quantitative, separates species | Column may adsorb or disrupt aggregates |
| Dynamic light scattering | Size distribution | Fast, no column | Biased toward large particles |
| A340 turbidity | Scattering | Very simple | Not species-specific |
| Thioflavin T | β-sheet fibrils | Specific to amyloid-like | Misses amorphous aggregates |

## Is SEC useful for short peptides?

-   For peptides below a few kDa, monomer and small oligomers may not be well resolved on typical columns.
-   Hydrophobic or charged peptides can stick to the column, giving tailing or false losses.
-   SEC is most useful for longer, aggregation-prone peptides and peptide conjugates.

## How does Sable document lots?

There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.

## Frequently asked questions

### What elutes first in SEC?

The largest species, such as aggregates; monomer elutes later.

### What does SEC-MALS measure?

Absolute molar mass of each eluting peak, independent of column calibration.

### Is SEC the same as reversed-phase HPLC?

No. SEC separates by size under mild conditions; RP-HPLC separates by hydrophobicity.

## Related

-   [Peptide aggregation in assay solutions](/guides/peptide-aggregation-in-assay-solutions)
-   [RP-HPLC retention](/guides/rp-hplc-retention-and-peptide-hydrophobicity)
-   [Circular dichroism](/guides/circular-dichroism-for-peptide-secondary-structure)
-   [Surface adsorption](/learn/tech-notes/peptide-surface-adsorption)

Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.

Key facts (summary for AI and search tools)

-   SEC: large elutes first
-   Report: % monomer, % HMW species
-   References: PubMed 24816223, 31282880
-   Updated 2026-10-16