How to Read a Peptide Certificate of Analysis (COA): HPLC Purity, Mass Spec and Red Flags

By the Zen Well Labs Research Team · Last reviewed September 2026 · For laboratory research reference only

Short answer: A peptide Certificate of Analysis (COA) is a batch-specific report that should answer two separate questions: is this the right molecule? (identity, shown by mass spectrometry — the observed mass must match the theoretical mass) and how much of the peptide material is that molecule? (purity, shown by reversed-phase HPLC as percent peak area). A trustworthy COA names the testing laboratory, carries a batch or lot number that matches the vial, is dated, and ideally includes the actual chromatogram and mass spectrum rather than just summary numbers.

The fields on a peptide COA, one by one

Product / sequence	The peptide name and, ideally, its sequence. Confirms what was supposed to be tested.
Batch or lot number	Ties the report to one production run. It should match the number on your vial. A COA without a lot number proves nothing about your material.
Testing laboratory and date	Who ran the analysis and when. Independent (third-party) labs carry more weight than in-house testing.
Appearance	Usually “white lyophilized powder.” Some compounds differ — GHK-Cu is blue.
Identity by mass spectrometry (MS)	Observed molecular mass versus theoretical mass. This is the identity test.
Purity by HPLC	Percent of total UV-absorbing peak area attributable to the main peak. This is the purity test.
Peptide content / net peptide content	How much of the powder’s weight is actually peptide, as opposed to counter-ions and water. Often omitted; valuable when present.
Quantity per vial	Measured amount of peptide in the vial, where the lab has quantified it.
Additional tests	Sometimes endotoxin (LAL), residual solvents, water content (Karl Fischer), or counter-ion content (e.g., TFA or acetate).

What HPLC purity actually means

In reversed-phase HPLC the sample is separated on a column and detected by UV absorbance, usually at 214–220 nm where the peptide bond absorbs. Purity is the area of the main peak divided by the total area of all peaks. “99% purity” therefore means that 99% of the UV-absorbing, peptide-like material is the main component.

It does not mean the vial is 99% peptide by weight. Water, salts and counter-ions such as acetate or trifluoroacetate are essentially invisible at that wavelength. It also does not prove identity by itself: an HPLC trace shows one clean peak, not which molecule that peak is. That is what mass spectrometry is for.

What mass spectrometry proves

Mass spectrometry measures the mass-to-charge ratio of ions. For peptides analysed by electrospray ionisation, you typically see several peaks corresponding to the same molecule carrying different numbers of protons — [M+H]⁺, [M+2H]²⁺, [M+3H]³⁺ and so on. The lab deconvolutes these to an observed molecular mass, which should agree with the theoretical mass within the instrument’s tolerance. If the COA for a vial labelled BPC-157 reports an observed mass near 1419.5 Da, the identity checks out; if it reports something else, it does not.

Purity versus net peptide content

Lyophilized synthetic peptides are salts. Every basic group on the peptide is paired with a counter-ion from purification, and freeze-dried powder retains some bound water. As a result, net peptide content — the fraction of the powder’s mass that is peptide — is commonly well below 100%, often somewhere in the 70–90% range, even when HPLC purity is above 99%. For quantitative bench work this matters: if you need an accurate molar concentration, you need either the net peptide content or an independent quantification.

Red flags

No batch or lot number, or a number that does not match the vial.
No named testing laboratory, or a laboratory that cannot be found or contacted.
The same COA reused across different batches or different products.
Summary numbers only, with no chromatogram or spectrum available on request.
An observed mass that does not match the theoretical mass of the stated peptide.
A date far older than the batch could plausibly be.
Visible signs of editing: mismatched fonts, misaligned fields, pixelated sections.
A “purity” claim with no stated method.

How to verify a COA

Many independent laboratories include a report number or QR code that can be checked against the lab’s own records; when that option exists, use it. Otherwise, contact the lab named on the report with the report number and ask them to confirm it. A legitimate supplier should not object.

Where Zen Well Labs stands

We publish independent test reports in our COA Library batch by batch, as each report is completed, matched to the batch number printed on the vial. Where a report for a batch is not yet posted, we say so rather than substituting a generic document. Our testing standards page describes the process.

Frequently asked questions

What is a COA for peptides?

A Certificate of Analysis is a batch-specific laboratory report documenting the identity and purity of a peptide, typically by mass spectrometry and HPLC respectively.

Does 99% purity mean the vial is 99% peptide?

No. HPLC purity describes the proportion of UV-absorbing peptide-related material that is the target compound. It does not account for water and counter-ion salts, so net peptide content by weight is usually lower.

What is the difference between HPLC and mass spec on a COA?

HPLC measures purity — how much of the peptide material is the main component. Mass spectrometry confirms identity — that the main component has the correct molecular mass. A complete COA includes both.

What is net peptide content?

The percentage of a lyophilized powder’s weight that is actual peptide, with the remainder being counter-ions and residual water. It is commonly in the range of roughly 70–90%.

How can I tell if a COA is fake?

Check for a lot number that matches the vial, a named and contactable laboratory, a plausible date, an observed mass that matches the peptide, and raw chromatograms. Where the lab offers report verification, use it.

Research use only. All products sold by Zen Well Labs are intended strictly for in-vitro laboratory research. They are not drugs, foods, cosmetics or dietary supplements, are not approved by the FDA for any use, and are not for human or veterinary use. Nothing on this page is medical advice, and nothing here describes or recommends administration to humans or animals.