How to Read a Peptide Certificate of Analysis

RESEARCH USE DISCLAIMER
Crown Peptides supplies research compounds for laboratory use only. Our products are not intended for human consumption and are not sold, marketed or labelled for the diagnosis, treatment, cure or prevention of any disease.

What a Certificate Is Actually For

A certificate of analysis answers two separate questions, and it is worth being clear that they are separate.

The first is identity: is this the compound it claims to be? The second is purity: how much of what is in the vial is that compound, and what makes up the rest? A certificate that answers only one of those is doing half a job, and the half it leaves out is usually the more important one.

Mass Spectrometry: Is It the Right Molecule?

Mass spectrometry measures molecular weight with considerable precision. Every peptide has a calculated mass determined by its amino acid sequence, and the measured mass should match it.

This is the identity test, and it is the one people skip over. A vial could be 99% pure and still contain the wrong peptide entirely — purity says nothing about what the substance is. The mass spec result is what rules that out.

When reading one, check that the observed mass matches the theoretical mass for that specific compound. Be aware that salt forms shift the figure: a peptide supplied as an acetate salt weighs more than the free peptide, and a copper complex such as GHK-Cu weighs more than the tripeptide alone. A mismatch is not automatically a red flag, but it should be explicable.

HPLC: How Much of It Is There?

High performance liquid chromatography separates everything in the sample by how strongly it sticks to a column, producing a chromatogram — a trace with peaks. The target peptide is the main peak, and purity is calculated as that peak’s area against the total of all peaks.

So 98% purity means the main peak accounts for 98% of the total area. The remaining 2% is everything else that came off the column: related peptides, residual solvents, fragments.

This is why the chromatogram itself matters more than the number derived from it. A single clean peak with a flat baseline is a very different picture from a main peak with several small ones clustered beside it, even when both calculate to the same percentage.

Deletion Sequences: The Impurity That Hides

This is the one worth understanding properly, because it is the hardest thing to catch.

Peptides are built one residue at a time. If a single coupling step fails, the chain continues without that residue, producing a molecule almost identical to the target but one amino acid short. These are deletion sequences.

They are difficult to detect because they behave almost identically to the real thing. They elute at nearly the same point on the column, so their peak sits immediately beside the main one — sometimes as a shoulder rather than a separate peak at all. A purity figure can absorb them without ever revealing them.

Seeing the actual chromatogram is the only reliable way to notice. A slight asymmetry on the main peak is worth more scrutiny than a headline percentage.

What a Complete Certificate Includes

The batch number, matching the one printed on the vial you received. A certificate for a different lot tells you about a different batch of material.

The compound name and sequence, so identity can be checked against the mass.

The test method, not merely the result. HPLC conditions vary, and a purity figure without its method is not comparable to another.

The chromatogram and mass spectrum themselves, not just numbers transcribed from them.

The date of testing and the laboratory that performed it.

Questions Worth Asking

Is the certificate for my batch? A generic certificate reused across lots is not evidence about the vial in your hand.

Can I see the chromatogram? A supplier quoting a percentage but unwilling to show the trace behind it is asking to be trusted rather than checked.

Was identity tested at all? Purity alone does not establish what the compound is.

Is the testing independent? In-house results are not worthless, but third-party analysis carries more weight.

Our full COA library publishes complete certificates rather than summary figures, and our testing guide covers how to vet a supplier more broadly.

Frequently Asked Questions

What does a certificate of analysis show?

Two things: identity, usually by mass spectrometry, and purity, usually by HPLC. A complete certificate also names the batch, the method, the date and the testing laboratory.

Is 99% purity good?

It is a reasonable figure, but the number alone is incomplete. What matters is what the remaining percent consists of and whether the chromatogram shows a clean single peak or a cluster.

What is a deletion sequence?

A peptide missing one amino acid because a coupling step failed during synthesis. It elutes very close to the target, so it can hide inside a purity figure without being obvious.

Why does the mass on the COA not match what I calculated?

Usually the salt form. Acetate salts and metal complexes such as GHK-Cu weigh more than the free peptide, so the certificate may quote a different figure to a sequence-only calculation.

Should a COA be batch specific?

Yes. The batch number on the certificate should match the one printed on your vial, otherwise it describes different material.