How to Read a Peptide Certificate of Analysis (COA)

A peptide certificate of analysis (COA) is the primary quality document accompanying a research-grade reference vial. Reading it well is a foundational laboratory skill — the difference between reproducible bench work and a study confounded by variable input material.

The most-cited number is HPLC purity, typically reported as an area percentage from a reverse-phase HPLC chromatogram. Research-grade reference peptides should report purity above 98%, with pharmaceutical-grade often reported above 99%. The chromatogram itself is more informative than the single number — a clean baseline with one dominant peak is what quality reference material looks like.

Mass-spectrometry identity confirmation appears next. The observed mass should match the theoretical monoisotopic or average mass of the peptide within the instrument's stated tolerance. A significant mass mismatch indicates either a synthesis error or a labelling error and should be flagged before use.

Moisture content matters for accurate mass-based dosing. Lyophilised peptides typically report moisture between 2% and 6%; higher values mean the peptide mass in the vial is lower than the labelled figure by a proportional amount. Acetate (or trifluoroacetate) content should also be listed, since these counter-ions contribute to the mass of the powder without contributing to the pharmacologically active peptide.

Appearance, solubility notes and stability guidance complete the COA. Together they describe what you should see in the vial, what solvent is recommended for reconstitution and what stability window to plan around. Any documented reconstitution or storage guidance should be recorded alongside the assay metadata.

This article is intended as educational reference material for laboratory researchers. Every batch used in published work should be handled in line with institutional protocols and the supplier's batch-specific COA.