A batch of material can arrive with several documents, and they are not versions of one another. Each answers a question the others do not, and knowing which is which saves you from reading a document as evidence of something it was never about.
The certificate of analysis
The summary document. It names the batch, lists what was measured, gives the result for each parameter and the method that produced it, and carries a date and a signature.
It is the document people mean when they say a peptide "has a COA", and the one most often produced on request. That makes it worth being precise about its limits.
It establishes what someone found when they tested this batch. It does not establish that the material in front of you is that batch, which is what the number on the label is for, and it says nothing about parameters it does not list. The fields are covered one by one in our note on reading a certificate and the abbreviations in the glossary.
The chromatogram
The raw trace behind the purity figure: detector response against time, with the target as the large peak and everything else the method detected as smaller ones.
A certificate can report 99.2 percent without showing you where the other 0.8 percent sits. The trace shows it. A shoulder on the main peak means the method barely separated something; several small peaks spread across the run are a different picture from one peak sitting right beside the target, which in synthetic peptides often corresponds to a deletion sequence differing by a single residue.
The axes are part of the evidence. A trace with no scale on the time axis cannot be compared against anything, and an image too low in resolution to read the labels is a picture of a chromatogram, not a chromatogram.
What it cannot tell you is what any of those peaks are. Chromatography sorts by how strongly things stick to a column, not by identity. (Reference: Dong, 2006) It also cannot show you anything the detector did not see: at 214 nm a peptide bond absorbs, but salts and water pass through invisibly.
The mass spectrum
The identity evidence. The instrument measures mass-to-charge ratios, and the measured mass is compared against the mass calculated from the intended sequence. (Reference: Fenn et al., 1989)
It is the only one of these documents that addresses what the molecule is. A chromatogram showing one clean peak is compatible with a pure sample of entirely the wrong compound, and only a mass measurement closes that gap. Our note on mass spectrometry covers how the comparison works.
Its blind spot is the mirror image: a mass spectrum can confirm the mass is right while saying little about how much else is present. Two molecules of identical mass are indistinguishable by mass alone, which is why identity and purity are read together.
The safety data sheet
A hazard communication document, standardised into sixteen sections by the Globally Harmonized System, covering identification, hazards, composition, first aid, handling, storage, toxicology and disposal in a fixed order. (Reference: UNECE, 2023) The order is fixed so that anyone can find the same information in the same place, whoever wrote the sheet.
It is often mistaken for a quality document. It is not. An SDS describes a substance as a class, not a batch, so two batches of very different purity carry identical sheets. It tells you how to handle the material safely and nothing about what is in the vial.
The label
The shortest document and the one that ties the others to a physical object. Compound name, batch number, quantity, storage condition, and a statement of what the material is for.
The batch number is the whole point. It is the thread connecting a certificate to something you can hold, and without it the paperwork describes material in the abstract. Storage conditions belong here for the same reason: a peptide degrades by known routes that proceed with time and temperature, so a document that never reaches the person storing the vial is not much use. (Reference: Manning et al., 2010) Our note on storage covers the reasoning.
What no document establishes
None of these proves the material is the same today as when it was tested. A certificate is dated because a result belongs to a moment, and the gap between that date and the vial in your hand is filled by storage and shipping, not by paperwork.
Nor does any of them say anything about a second vial. Testing is done on a batch. A document for batch CDX-1017 tells you nothing about CDX-1018, which is why the batch number is checked before anything else on the page.
Which ones you can reasonably ask for
A batch-specific certificate and a label carrying the batch number are the minimum, and any supplier can produce both. The safety data sheet is standard and costs nothing to send, since it belongs to the compound and not to the batch.
The raw chromatogram and mass spectrum are a larger ask, because they come from the laboratory's own instrument files, not from a template. A supplier who has them will send them. One who only ever has a summary is telling you something about where the summary came from.
How they fit together
The label says which batch. The certificate says what was found in that batch and by what method. The chromatogram shows the purity result instead of asserting it. The mass spectrum says the main component is the intended molecule. The safety data sheet describes the compound class, whatever the batch.
A supplier who provides all five has not proven their material is good. They have made it possible for you to check, which is a different thing and the only one a document can do.
Research use only
All products sold by Codex Research are strictly for laboratory research and development. They are not for human or animal consumption and are not intended to diagnose, treat, cure, or prevent any disease.
Frequently asked questions
What documents should come with a research peptide?
A batch-specific certificate of analysis, ideally the chromatogram and mass spectrum behind it, a safety data sheet, and a label carrying the batch number and storage condition.
Is a safety data sheet a quality document?
No. An SDS describes a substance as a class and covers handling, storage, first aid and disposal. Two batches of very different purity carry identical sheets, so it says nothing about what is in a particular vial.
Why ask for the chromatogram if the certificate already gives a purity figure?
The figure is a single number; the trace shows where the remainder sits. A shoulder on the main peak, or one small peak beside it, is a different picture from impurities spread across the run.
What does a mass spectrum add?
Identity. Chromatography separates by retention, not by what a compound is, so a clean single peak is compatible with a pure sample of the wrong molecule. Comparing measured mass against the mass calculated from the sequence closes that gap.
Does a certificate prove the material is still at that purity?
No. A result belongs to the date it was measured. What happened between that date and the vial in your hand is a matter of storage and shipping, which no document covers.
Why does the batch number matter more than the figures?
Because it is what ties the paperwork to a physical object. A document for one batch says nothing about another, so if the number on the label does not match, the figures describe different material.
References
- Dong, M.W. (2006). Modern HPLC for Practicing Scientists. Wiley.
- Fenn, J.B., Mann, M., Meng, C.K., Wong, S.F., & Whitehouse, C.M. (1989). Electrospray ionization for mass spectrometry of large biomolecules. Science, 246(4926), 64-71.
- Manning, M.C., Chou, D.K., Murphy, B.M., Payne, R.W., & Katayama, D.S. (2010). Stability of protein pharmaceuticals: an update. Pharmaceutical Research, 27(4), 544-575.
- UNECE (2023). Hazard communication: Safety Data Sheets (SDS). In Globally Harmonized System of Classification and Labelling of Chemicals (GHS). United Nations.