How to read a peptide Certificate of Analysis (COA)

A COA is a batch-level document, not a product-level document. That distinction is the most important thing to understand before reading one.

Two vials of the same peptide from the same vendor can belong to different manufacturing lots with different purity profiles, different water content, and different counter-ion ratios. A real COA is generated from tests performed on the specific lot that produced the specific vial being sold. A document that covers an entire product line is not a COA in the meaningful sense — it is marketing material with the word "Certificate" on it.

A legitimate research supplier produces a COA per batch, with a batch number that matches the label on the vial. The analytical tests behind it are usually run by a third-party analytical lab, though in-house testing also appears in the market and is not automatically disqualifying.

Every field on a well-prepared COA answers a specific question about the material. Here is what each one is asking and how to read the answer.

Product identification

Compound name, CAS number, sequence, molecular formula, molecular weight. This is the identity pillar. The COA must name exactly what the vial contains. A missing CAS number or sequence is the first sign that the document is not rigorous.

Lot number and manufacturing date

The batch-specific traceability back to a production run. A COA without a lot number cannot be tied to the vial in hand, which defeats the purpose of having a COA at all.

Appearance

Physical description of the lyophilized powder — usually "white to off-white lyophilized powder." A quick visual check against this description when the vial arrives is the first sanity check before anything else.

Identity confirmation by mass spectrometry

Mass spectrometry, or MS, measures the exact molecular mass of the compound in the vial. The COA reports the observed mass, which should match the theoretical mass for the peptide within a narrow tolerance. For BPC-157, that is roughly 1,419 Da. A large discrepancy between observed and theoretical mass means the vial does not contain what the label says it contains.

Purity by HPLC

High-performance liquid chromatography, or HPLC, separates the sample into its individual components and measures how much of the total is the target peptide versus impurities. The purity percentage on a COA is the area under the main peak expressed as a percentage of all peak area in the chromatogram.

Research-grade peptides should be greater than 95% pure. High-grade is 98% or above. A COA that reports purity without an attached chromatogram gives the number without the evidence — the chromatogram is how the number is actually substantiated.

Peptide content

Peptide content and peptide purity are different measurements, and the distinction catches a lot of buyers off guard. Purity is how clean the peptide fraction is. Content — sometimes called net peptide — is how much of the vial's total mass is actually peptide after water, counter-ions, and salts are accounted for.

A vial labeled 10 mg with 80% peptide content delivers roughly 8 mg of actual peptide. For research work where dose accuracy matters, peptide content is often the more useful number.

Water content by Karl Fischer

Karl Fischer titration measures the residual moisture in the lyophilized powder. Typical range is 1 to 5 percent. Too much water suggests incomplete lyophilization, which affects both potency and shelf life.

Residual solvents

Leftover manufacturing solvents — typically acetonitrile, trifluoroacetic acid, or methanol. These should sit within ICH Q3C guideline limits. Most COAs report these as trace amounts or below the limit of detection.

Counter-ion or acetate content

Most research peptides are supplied as acetate salts. The counter-ion takes up mass in the vial, which is why peptide content sits below 100 percent of the stated weight. The counter-ion figure feeds directly into any peptide-content calculation.

Endotoxin, when applicable

For material intended for certain animal-model work, endotoxin levels are measured by the Limulus Amebocyte Lysate (LAL) test and reported in endotoxin units per milligram. Not every COA includes it — endotoxin testing is selective, driven by the research application.

Analyst signature and date

A COA that is not signed off by a named analytical chemist and dated is an uncontrolled document. That field is easy to overlook, and its absence is diagnostic.

Four methods do most of the work on a peptide COA. Each answers a specific question.

Some higher-grade COAs also include amino acid analysis or NMR data. Both are optional and signal a more rigorous analytical program.

Most COA evaluations collapse to six questions. If every answer is yes, the document is reliable. If any answer is no, ask for a better document or find a different supplier.

• ●Does the COA name a specific lot number that matches the vial label?
• ●Is HPLC purity reported at 95 percent or higher, with a chromatogram or trace attached?
• ●Is the mass-spec observed mass within acceptable range of the theoretical mass?
• ●Is peptide content (net peptide) stated as a separate number from purity?
• ●Is water content reported?
• ●Is the COA signed by an analytical chemist and dated?

The checklist is short on purpose. It is designed to be applied in under a minute per document.

Four patterns account for almost every bad COA in the market.

The fastest way to develop an instinct for COA reading is to look at a few real ones. The BPC-157 and retatrutide product pages both link to current batch-specific COAs that carry the fields described above. Reading the checklist with a real document in front of you is a useful second pass.

For the research-compound context behind those COAs, the BPC-157 research guide covers the mechanism and the tissue types studied, and the retatrutide explainer covers the triple-agonist mechanism and Phase 2 and Phase 3 data.

Reading a COA well is necessary but not sufficient for evaluating a research-peptide vendor. The full picture is the intersection of documented purity, batch consistency over time, cold-chain integrity in shipping, and honest regulatory framing.

The best peptide vendors guide covers the broader evaluation framework — the COA is one leg of a three-legged stool, not the whole thing.

• ●A COA is batch-specific, not product-specific.
• ●HPLC purity above 95 percent, with a chromatogram attached.
• ●Peptide content is different from purity, and often more useful for dose accuracy.
• ●Mass spec confirms identity; observed mass should match theoretical.
• ●The six-point checklist applies in under a minute.
• ●Identical COAs across lots, missing chromatograms, in-house only without audits, and gated COAs are the four recurring red flags.