How to read a peptide COA: purity, identity and sterility

The question

A peptide certificate of analysis, or COA, is useful only when you know which question each result answers. A prominent purity percentage does not, by itself, tell you the amount of peptide in a container, whether a sample is sterile, or whether a substance has been shown to help people. Reading the smaller fields often tells you more than reading the largest number.

Start with a simple habit: write down what the report actually measured before deciding what it means. This guide explains five separate questions and a practical way to keep them separate. It does not certify any supplier or establish that a research material is suitable for personal use.

1. Does this report belong to this material?

Before looking at a result, compare the product name, chemical form and batch identifier with the material being described. Look for a sample identifier, reporting laboratory, test date, method and result units. If the report is a cropped screenshot, ask for the complete document. If the laboratory offers a verification service, use its independently located contact details or verification page.

This is an editorial document-reading checklist, not a guarantee of authenticity. A genuine report about one submitted sample does not automatically establish the contents of every container sold under the same product name. The missing question may be how the sample was collected and connected to the batch. A report without that connection is harder to interpret even if its measurements are technically sound.

2. Identity: what was detected?

Identity and purity are different measurements. Bachem’s technical guide describes mass spectrometry as a way to measure molecular weight and comparison with a reference sample as another identity tool. A purity percentage alone does not replace identification. Ask whether the report identifies the named substance or merely displays a chromatographic peak. Bachem quality-control guide.

For a blend, make that question plural. Which components were identified? A document headed with a blend name may not answer every ingredient-level question. Read the scope of the test rather than assuming that the title describes everything the laboratory examined.

3. Purity: a percentage of what?

HPLC separates components under specified conditions. In the common UV method described by Bachem, the purity calculation compares the main peak area with the total detected peak area. The result depends on the analytical method; it is not a universal inventory of everything in the container. Bachem’s explanation of peptide purity.

Here is a deliberately hypothetical example. A report says “99% HPLC purity” and lists no sterility or endotoxin test. The defensible reading is that a particular analytical purity result was reported. The report has not supplied a sterility result. It has not supplied an endotoxin result either. Those blanks should remain blanks in your notes; do not mentally turn them into passes.

That habit also prevents a subtler mistake: treating two percentages from different methods as a head-to-head ranking. Before comparing them, establish that they answer the same question under comparable conditions.

4. Content: how much material does the number describe?

Net peptide content is a separate concept. Peptide solids can include water and counterions, so chromatographic purity and the proportion of peptide in the solid need not match. Bachem explicitly distinguishes these measures. Care and handling of peptides.

On a report, inspect the units and the definition of the assay. A percentage, an amount per container and a total blend amount are different statements. Avoid reconstructing an unreported result by multiplying unrelated label numbers. If the method and reporting basis are unclear, the useful next question is what the laboratory means by “content,” not whether the printed percentage looks impressive.

5. Microbiological quality: what was actually tested?

Sterility testing and bacterial endotoxin testing address different hazards. A chromatography result cannot stand in for either. FDA maintains separate guidance on pyrogen and endotoxin testing, including appropriate testing approaches for regulated products. This guidance is not a certification of research catalogs. FDA guidance, March 2026.

Even a sterility test has limits. FDA explains that testing is one part of a broader contamination-control system and does not exhaustively assess batch sterility. Manufacturing controls and the meaning of the tested sample matter alongside the final result. FDA production and process-control questions.

Turn the report into a short evidence note

Use five lines: batch connection; identity; analytical purity; content; microbiological tests. Beside each, record the reported result and its method, or write “not provided.” Keep supplier statements in a separate column from laboratory findings. This makes gaps visible without guessing whether an unreported test would pass or fail.

The final question sits outside the COA altogether: what evidence supports the intended medical claim? An analytical document is not a clinical trial or an FDA approval. FDA also makes clear that compounded drugs are not FDA-approved and are not reviewed for safety, effectiveness and quality before marketing. Research listings should not be treated as equivalent to those medicines. FDA on compounded drugs.

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