Your Peptide COA Says 99% Pure. Here’s What That Actually Means

A certificate displays 99% purity. Before asking whether that is high enough, ask: 99% of what?

Does it describe the share of an integrated chromatographic signal assigned to a main peak? A mass fraction established by a validated quantitative method? Something else? Until the method and calculation are clear, the apparent precision can hide an ambiguous claim.

The correct response is not to dismiss the document. It is to read it as a report of particular tests performed on a particular sample.

Start with the question the test can answer

High-performance liquid chromatography separates components under specified conditions. In a common area-normalization calculation, the area assigned to the main peak is divided by the total integrated peak area and multiplied by 100.

Consider a hypothetical chromatogram in which the main peak accounts for 99 of 100 integrated area units. That produces a 99% area result. It does not, by arithmetic alone, establish that 99% of everything in a vial is the intended peptide by mass.

The distinction depends on the method: which components were detected, how they responded, whether the separation resolved them and which signals were integrated. FDA's analytical guidance emphasizes specificity, selectivity and the ability to measure relevant components without interference. An analytical number is strongest when those capabilities have been demonstrated for its intended purpose. 12

The trace is useful when the report makes clear what the method could detect—and what it could miss.

Identity and amount need their own evidence

Identity asks whether the material is the intended compound. Quantity asks how much of that compound is present. Purity asks about relevant impurities under a defined method. These questions overlap, but they are not interchangeable.

Mass spectrometry can provide valuable evidence about molecular mass and identity. It does not automatically turn an uncalibrated signal into a reliable measurement of peptide content. A quantitative claim needs an appropriate method, standards, calculation and reporting basis.

A vial's total powder mass can also include material other than the peptide component of interest. Water, counterions and formulation ingredients can matter. The report should make clear whether an amount is expressed on an as-is, dried, free-base or other defined basis, rather than leaving readers to assume all numbers describe the same thing.

The method and reporting basis must match the claim being made. Validation for one purpose does not automatically establish fitness for another. 1

Chemical names can expose a real inconsistency

FDA's July 2026 compounding presentation provides a concrete example. In a table reviewing two withdrawn BPC-157 nominations, the agency showed certificates describing BPC-157 acetate alongside identifiers and molecular information matching the free base. 3

That does not mean every certificate for BPC-157 is false. It shows why the chemical form, identifier, formula and assay basis need to agree.

The useful reading habit is to follow the document's internal logic. If the title, substance identifier and calculated content refer to different forms, a favorable purity result does not resolve the mismatch.

Contamination and stability are different questions again

A chromatographic purity percentage is not a sterility test, an endotoxin result or a demonstration that material remained unchanged during storage. Those attributes require suitable methods and an appropriate sampling and quality system.

A result can be reassuring about the attribute tested while leaving other attributes unexamined. “Not tested” should not be silently converted into “passed.” Equally, a missing test on a particular document does not establish that contamination is present; it identifies information that the document does not supply.

Stability claims also need a basis. FDA's laboratory-control guidance distinguishes a genuinely stability-indicating method from an assay that cannot separate the intended material from relevant degradation products or interference. A date on a certificate does not, by itself, establish a shelf life under every shipping or storage condition. 2

Match the paper to the material

Even a technically sound report loses relevance when the connection to the supplied lot is unclear.

For a laboratory procurement review, the report should identify the sample and lot, the testing organization, the methods, the dates, the results and the applicable acceptance criteria. A buyer should be able to determine whether the document concerns the supplied finished material or a different stage of production.

An outside laboratory can test the sample it receives. That does not, by itself, establish how representative the sample was, what happened to it before testing or whether every unit subsequently sold matches it. Those links between the report and the material need documentation too.

Read the conclusion narrowly enough to use it

Read a COA against four questions: What is the material? How much is present? Which relevant impurities or contaminants were assessed? Does the tested sample match the supplied lot and the needs of the experiment?

That is more useful than ranking suppliers by a single decimal place. A report showing 99.1% is not automatically more informative than one showing 98.9% if the former does not explain its method, analyte or sample.

Good documentation reduces uncertainty about laboratory material. It does not demonstrate clinical benefit, authorize human use or establish that a research product is interchangeable with an approved medicine.

The important number on a COA is not always the largest percentage. It is the result that answers the question the experiment actually requires.

Sources

1. FDA Q2(R2), Validation of Analytical Procedures.
2. FDA CGMP laboratory controls questions and answers.
3. FDA July 2026 compounding presentation slides.