How to Read a Peptide Certificate of Analysis
A Certificate of Analysis (COA) is the document that describes what is actually in a batch of peptide material. For anyone working with peptide ingredients — formulators, quality teams, or technical staff — knowing how to read a COA is a core skill. This article walks through the typical sections and explains what each number means.
Batch Identity
The top of a COA identifies the material: product name, peptide sequence or INCI name, batch or lot number, manufacturing date, and quantity. The batch number matters because quality data is batch-specific — a COA describes one batch, not the product in general.
Purity: The Headline Number
The most visible value on a COA is purity, usually determined by HPLC. Purity is expressed as a percentage (for example, 98.5%) and represents the fraction of the material that is the target peptide. The remainder consists of impurities: truncated sequences, oxidation products, salts, and residual solvents. High purity does not automatically mean high quality — the impurity profile matters too, which is why serious suppliers report more than a single number.
Peptide Content
Purity and peptide content are different things. Purity refers to the fraction of the target peptide among peptide species; peptide content refers to how much of the powder’s weight is actually peptide versus counter-ions and water. Many peptides are supplied as salts (typically acetate or trifluoroacetate), so peptide content can be meaningfully lower than purity. Both values should be read together.
Identity Confirmation
A COA should confirm identity, not just purity. Mass spectrometry data showing the observed molecular weight matching the theoretical value is the standard evidence. Amino acid analysis can additionally verify the composition. If a COA reports purity without identity data, it tells only half the story.
Other Typical Sections
- Residual solvents — limits for solvents used in synthesis, such as acetonitrile or TFA.
- Water content — measured by Karl Fischer titration; affects storage and stability.
- Appearance and solubility — quick physical checks.
- Microbiological data — for food-grade materials, microbial counts and pathogen limits.
- Storage conditions and retest date — how long the batch remains within specification.
Red Flags to Notice
Experience helps, but some patterns are worth flagging: a COA without a batch number, purity claimed without an analytical method, identity data missing, or specifications that never vary between batches. These do not prove a problem, but they are worth questioning.
Original educational article. For background on peptide analysis, see HPLC — Wikipedia and Mass spectrometry — Wikipedia.