How to read a certificate of analysis

A certificate of analysis (COA) is a laboratory's record of what a specific batch of material was tested for, how, and with what result. Reading one well means checking that it is tied to the batch in front of you, that it names the methods and the laboratory, and that its numbers can be independently confirmed — not simply that a purity figure looks high.

This page explains how to read any peptide certificate critically, including ours. It is written so the same checks apply to any supplier's document: a certificate only demonstrates quality if you can verify it, and verification is a skill worth having.

What a certificate of analysis is — and is not

A certificate of analysisCertificate of analysis (COA)A document reporting the analytical test results for a specific batch of material, issued by the laboratory that tested it.Full definition → is a report of measurements. For one identified batch it states what was tested, the method used, and the result obtained, signed off by the laboratory that did the work. It is evidence of testing, not a guarantee of fitness for any purpose.

It is not a marketing document, a label, or a substitute for traceability. A glossy page quoting "99% purity" with no method, no batch number and no laboratory named is a claim, not a certificate. The difference between the two is the whole subject of this page.

Two questions a good certificate lets you answer are distinct and both matter: what is this material (identity), and how pure is it (composition). A third — how much peptide is present — is a separate measurement again, covered in purity versus net peptide content.

The fields a certificate must contain

A complete certificate makes each of the following explicit. If a field is missing, that absence is itself information.

How to read an HPLC chromatogram

Most peptide purity figures come from reverse-phase HPLCReverse-phase HPLCThe most common HPLC mode for peptides, separating molecules by how strongly they interact with a non-polar column.Full definition →. The instrument separates the components of a sample so that each elutes from the column at a characteristic retention timeRetention timeThe time a component takes to travel through a chromatography column and reach the detector, characteristic under fixed conditions.Full definition →, producing a chromatogramChromatogramThe plot produced by a chromatography run, showing detector signal over time as separated components pass through.Full definition →: detector response plotted against time.

Reading a trace comes down to a few habits:

• Find the main peak. It is the tall, dominant peak — the target compound. Its retention timeRetention timeThe time a component takes to travel through a chromatography column and reach the detector, characteristic under fixed conditions.Full definition → should be consistent with the method.
• Look at the baseline. A flat, quiet baseline between peaks is a sign of a clean separation. A noisy or drifting baseline makes small peaks hard to judge.
• Count and size the impurity peaksImpurity peakAny peak on a chromatogram other than the main target peak, representing a component distinct from the intended compound.Full definition →. These are the smaller peaks before and after the main one. A single tall peak with a few tiny neighbours is cleaner than one main peak surrounded by many small ones.
• Check the separation. Impurity peaks that sit right on the shoulder of the main peak are harder to quantify than well-separated ones.

Chromatographic purityPurity (chromatographic)The percentage of the main peak's area relative to the total peak area on a chromatogram — a measure of composition, not quantity.Full definition → is then the area of the main peak divided by the total area of all peaks, expressed as a percentage. Because that figure depends on how the sample was detected, a purity number should always be reported with its method — the principle behind analytical method validation set out in ICH Q2(R2) ↗.

How to read a mass spectrometry result

Mass spectrometryMass spectrometryAn analytical technique that measures the mass-to-charge ratio of ionised molecules to confirm a compound's identity by its molecular weight.Full definition → answers a different question: identity. The instrument measures the molecular weightMolecular weightThe mass of one molecule of a compound, expressed in daltons (Da) — the value mass spectrometry checks against the expected figure.Full definition → of the ionised molecule, and a certificate reports the expected mass (calculated from the sequence) alongside the observed mass.

• A match confirms identity. When the observed molecular weight matches the theoretical value for the peptide's sequenceSequenceThe specific order of amino acids in a peptide, which defines its identity and its theoretical molecular weight.Full definition →, that is strong evidence the material is the intended compound.
• A match does not confirm purity or quantity. Mass spectrometry can identify the target molecule while impurities or a lower-than-labelled peptide mass go unmentioned. That is why it is read alongside the HPLC purity figure and, for content, amino acid analysis.

Red flags

Any one of these should prompt more questions before the certificate is treated as evidence:

• No batch number, or a number that does not match the vial.
• No manufacture or test date.
• No named testing laboratory, or one that cannot be contacted independently.
• One certificate reused across multiple batches — a certificate describes a single run, not a product line.
• An image-only document with no underlying chromatogram or data, so nothing can be checked.
• A purity figure quoted without a method.
• A laboratory that publishes no way to verify the result at source.

How to verify a certificate independently

Verification is what turns a certificate from a claim into evidence:

1. Match the batch number printed on the certificate to the number physically on the vial. If they differ, the document does not describe your material.
2. Contact or check the testing laboratory. An independent lab that hosts its own copy of the result — for example Janoshik Analytical ↗ — lets you confirm the figures were not altered between the lab and the supplier.
3. Read the method, not just the number. Confirm the purity figure states its technique and that identity is supported by mass spectrometry.
4. Cross-check the dates so the test post-dates manufacture and is recent enough to be meaningful.

A worked example

Here is one of our own published third-party results, read field by field. The purity figure and laboratory are real and independently verifiable; the batch number and dates live on the laboratory's own certificate, linked below.