How to Read a Peptide COA: Purity, HPLC, and Specification Fields

What a COA Actually Is

A certificate of analysis (COA) is a batch-specific document issued by the manufacturer or testing laboratory. It records the results measured for one production lot, not a generic claim about a product family. Treat the COA as the primary evidence that a specific vial matches its specification.

Identity: Confirming the Right Molecule

Identity is usually confirmed by mass spectrometry, which verifies the molecular mass of the peptide. A correct mass confirms you received the intended sequence rather than a related compound. This field is the foundation for trusting every other result on the document.

Purity by HPLC

HPLC (high-performance liquid chromatography) purity is reported as the percentage area of the target peak in the chromatogram. A higher percentage means fewer detectable impurities. The COA should state the method, the column or gradient where relevant, and the purity value for the lot.

Assay and Peptide Content

Purity (HPLC area percent) and assay (actual peptide content) answer different questions. Assay tells you how much active peptide is present by mass, accounting for bound water and salts. Reviewing both helps you calculate how much material to use in a protocol.

Other Common Specification Fields

• Appearance: the expected form and color of the lyophilized material.
• Water content: often measured by Karl Fischer titration.
• Residual solvents: limits for any solvents used in production.
• Endotoxin or heavy metals: included where the specification requires them.
• Net mass: the labeled amount in the vial, used for reconstitution math.

Comparing Supplier Documentation

When evaluating suppliers, compare COAs on the same fields and the same methods. Consistent, lot-specific documentation is easier to audit than generic certificates. A supplier that can explain each field is usually easier to work with over time.

See our wholesale peptide supply for lot-specific COAs, and browse research peptides by category.

All products are intended for research and laboratory use only.