- A Certificate of Analysis is only meaningful when it is tied to the batch in your hand – a generic “sample CoA” tells you about a different vial.
- Batch numbers connect four things: the label, the certificate, the supplier’s records and your own lab notebook.
- Purity and identity are separate questions answered by separate methods; a credible CoA reports both.
- Traceability is what makes research reproducible – and what lets you rule out the material when an experiment misbehaves.
Every vial that leaves a peptide supplier carries an implicit claim: this is the compound named on the label, at roughly the stated quantity, at the stated purity. A Certificate of Analysis (CoA) is the document that turns that claim into evidence. But a CoA is only as good as the link between the paper and the powder – and that link is the batch number.
This article explains why batch-specific documentation matters more than any headline purity figure, what a batch record should contain, and how a laboratory can build documentation into its routine without adding meaningful overhead.
What a batch actually is
In peptide manufacture, a batch (or lot) is a single production run: one synthesis, one purification, one lyophilisation cycle, one set of analytical tests. Two vials from the same batch were made together and tested together. Two vials from different batches – even of the same compound from the same supplier – were not.
That distinction is the whole point. Solid-phase peptide synthesis is a multi-step process in which small yield losses, incomplete couplings and side-reactions can accumulate differently from run to run. Purification then removes most of those impurities, but the exact profile of what remains – truncated sequences, deletion products, residual counter-ions – is specific to that run. A test result therefore describes one batch, not the compound in general.
Why a generic CoA is not documentation
It is common to see a supplier publish a single “representative” certificate for a product. It looks reassuring, and it is not worthless – it shows the supplier tests at all. But it cannot tell you anything about the vial you received unless the batch number on the certificate matches the batch number on your label.
A purity figure without a batch number is a marketing statement. A purity figure with a batch number is a data point you can audit.
For a researcher this matters in two directions. Forward, it determines whether you can trust the material going into an experiment. Backward, it determines whether you can investigate when a result looks wrong. If a series of assays drifts and you cannot say which batch each vial came from, the material is an unknown variable you can neither confirm nor exclude.
What a batch-specific record should contain
A useful certificate is short. The table below sets out the fields that carry real information, and what each one is for.
| Field | Why it matters |
|---|---|
| Compound name and stated quantity | Confirms the sample tested is the product described on the label, in the same format. |
| Batch / lot number | The link between certificate, label and supplier records. Without it nothing else can be verified. |
| Purity result and method | Usually reversed-phase HPLC, reported as a percentage of the main peak. The method matters as much as the number. |
| Identity confirmation | Typically mass spectrometry, showing the observed mass matches the expected molecular weight. Purity alone cannot prove identity. |
| Testing laboratory and date | Establishes independence and recency. A certificate from the manufacturer’s own bench is weaker evidence than one from a third-party lab. |
| Task or report reference | Lets the certificate be verified with the issuing laboratory if a question arises. |
Purity is not identity
The two most misread lines on a CoA are purity and identity, because they sound like the same thing. They are not. HPLC purity tells you what fraction of the material behaves like a single main component under the chromatographic conditions used. It says nothing about what that component is. Mass spectrometry answers the second question by measuring molecular mass. A sample can be 99% pure and still be the wrong peptide; a sample can be the right peptide at 92% purity. A credible batch record reports both, and a careful reader checks both.
Building traceability into routine practice
Documentation only protects an experiment if it is captured at the point of use. Three habits cover most of the value:
- Record the batch number when the vial is opened, not when the order arrives. The number belongs next to the experiment it was used in.
- File the certificate with the notebook entry – a photograph or PDF is enough – so the evidence travels with the data.
- Note reconstitution details against the same batch: diluent, volume, date, and storage after reconstitution. Handling is a variable too.
Where a supplier publishes its certificates in a searchable library, cross-checking takes seconds: find the batch number on the label, find the same number in the library, confirm the compound and quantity match. That check is worth doing on every delivery, not just the first.
When the paperwork does not match
A mismatch between label and certificate is not automatically a quality problem – it is frequently a filing error – but it is always a documentation problem, and it should be resolved before the material is used. Contact the supplier with the label batch number and ask for the corresponding certificate. A supplier who tests batch by batch will have it. A supplier who cannot produce it has told you something important about how they work.
In short
Batch-specific documentation is not bureaucracy. It is the mechanism that connects an analytical result to a physical vial, and it is the only reason a purity figure means anything at all. Insist on the batch number, check that it matches, file the certificate with your data, and the material stops being an unknown in your research.
Frequently asked questions
What is the difference between a batch number and a lot number?
They are the same thing. Both identify a single production run - one synthesis, purification and lyophilisation cycle tested together. Suppliers use either term.
Is a supplier's 'sample CoA' worthless?
Not worthless, but not documentation for your vial. It shows the supplier tests at all; only a certificate whose batch number matches your label describes the material you received.
Why does a CoA report purity and identity separately?
Because they answer different questions. HPLC purity measures how much of the sample is a single main component; mass spectrometry confirms that component has the expected molecular mass. A sample can score well on one and fail the other.
What should I do if the batch number on my vial is not in the supplier's library?
Contact the supplier quoting the label batch number and ask for the matching certificate before using the material. A batch-tested supplier will have it on file.
How long should I keep batch records?
For as long as any experiment that used the material remains live - in practice, file the certificate with the notebook entry so it is retained alongside the data it supports.
Reviews research content against current published literature and UK regulatory guidance, ensuring compound information is accurate, referenced and presented for research use only.
Research Use Only. This article is written for laboratory and analytical contexts. Nothing here is dosing guidance, medical advice, or a suggestion of human or veterinary use. All products are supplied strictly for research purposes.
