Working reference
How to read a certificate of analysis
An annotated walk-through of a typical research-peptide certificate, line by line, with the twelve things worth checking and the six things that are systematically absent. Click any highlighted line to jump to the note on it.
A certificate of analysis is a commercial document. In a regulated environment it is a controlled record with a defined content, a retention requirement and an audit trail; in the research-chemical trade it is whatever the issuer chooses to put on a page. Reading one well is therefore less about understanding chemistry than about noticing what is not there.
Below is a reconstruction of a typical certificate — a composite of documents the Journal has received, with no real company’s letterhead. The highlighted lines are annotated. The annotations are the useful part.
Composite certificate — reconstruction
- The issuing party A certificate issued by the seller is a self-declaration. One issued by a named independent laboratory is a third-party measurement. Both are useful; they are not the same claim, and a document carrying a seller’s letterhead and a laboratory’s layout is worth a second look.
- The batch number Check it against the vial, character by character, not against the box. Two of the determinations in the Journal’s dossier programme found a certificate batch number that did not match the vial it arrived with. In both cases the supplier’s remedy was to issue a corrected certificate, which is the wrong remedy: the question was which document described the vial.
- Nominal fill This is a fill mass, not a peptide mass. Conventionally, and lawfully, a research vial’s stated mass refers to the material filled, of which the peptide is a fraction — commonly 81–98% on the determinations the Journal has commissioned. Every calculation downstream inherits this.
- Date of analysis A certificate is a snapshot of a moment. A week after manufacture is unremarkable. An analysis date preceding the manufacturing date, or a gap of many months, is worth a question. So is a certificate whose analysis date is identical across several different lots.
- Retest date A retest date is not an expiry date and does not rest on a stability programme unless one was run. Where the interval is a round two or three years with no stability data cited, treat it as a commercial convention rather than a finding.
- Identity "Conforms by HPLC retention time" is the weakest identity claim in common use. Retention time is not specific: many closely related species elute close to the parent, and a match against an in-house standard of unstated provenance establishes very little. Identity confirmed by mass spectrometry is a stronger claim; identity confirmed by sequence is stronger again, and is almost never offered.
- The purity figure Note the decimal place. A single injection on a generic method does not support a claim to one decimal, and a figure of 99.2% presented without a method is a marketing number rather than a measurement. Across the Journal’s own determinations, supplier-stated figures have averaged around one to one and a half percentage points above independently determined ones, consistently in the same direction — which is the signature of an integration convention, not of dishonesty.
- The method line "RP-HPLC, UV 214 nm" is a partial method: it tells you the technique and the wavelength, which is more than most certificates give, and omits the gradient, the column and the threshold. 214 nm is appropriate for peptide-bond detection. A wavelength of 280 nm would see only species containing aromatic residues and should prompt a question.
- Gradient and integration threshold These two omissions are why the purity figure cannot be compared with anyone else’s. A shallow forty-minute gradient resolves impurities that a twelve-minute run buries under the main peak; a 0.1% threshold discards small peaks that a 0.05% threshold counts. Both are known to whoever produced the document and neither is commercially sensitive. Two of the twenty suppliers in the Journal’s programme now print both.
- Peptide content The most useful missing number. Content determines how much drug is in the vial, and therefore every dose calculation performed with it. It is determined by elemental nitrogen analysis or quantitative amino-acid analysis, costs several times a purity run, and is not offered as a standard release test by any supplier in the Journal’s programme.
- Water, counter-ion, residual solvent These three account for most of the gap between fill mass and peptide mass. Trifluoroacetate salts of basic peptides can carry ten to twenty per cent of total mass as counter-ion; a hygroscopic powder acquires water readily. None of the three is visible on a reversed-phase chromatogram, which is how a preparation can be simultaneously very pure and substantially not peptide.
- Sterility and endotoxin "Not applicable" is accurate for a research reagent and it is also the end of the conversation. Purity is a chemistry question; sterility is a microbiology question; a document that answers the first says nothing whatever about the second. No certificate in this trade that the Journal has seen reports either.
- The signature A named analyst with a legible name is a person who can be asked a question. An illegible mark, a scanned signature reused across lots, or no signature at all removes the only individual accountability the document contains. Two suppliers in the Journal’s programme print a named quality-assurance signatory; most do not.
The ten-minute check
In practice, a useful assessment of a certificate takes about ten minutes and consists of asking the following in order. Any single "no" is not disqualifying; three or four together describe a document that cannot support the weight the trade puts on it.
- Does the batch number on the certificate match the vial?
- Is there a gradient, a column and a wavelength?
- Is there an integration threshold?
- Are the reported items results, or specifications?
- Is the analysis date sensible relative to the manufacturing date?
- Is peptide content reported?
- Is water content reported?
- Is the salt form or counter-ion stated?
- Is the reference standard identified?
- Is there a named signatory?
- If the document names an independent laboratory, can that laboratory confirm the report number?
- Does anything on the page contradict anything else on the page?
Reading a certificate well is less about understanding chemistry than about noticing what is not there.
Cloned and template certificates
The document is the easiest thing in this trade to forge and the most trusted. A letterhead is an image, a report number is a string, and a summary page can be reproduced in a lunch break — whereas forging a chromatogram convincingly is real work. The Journal has documented certificates reproducing a genuine laboratory’s layout, report-number range and analyst signature, attached to lot numbers that laboratory says it never analysed.
The only structural fix is a lookup: a report number in, a yes or no out, published by the laboratory that issued it. The Journal has asked all four independent services whether they will offer one. Until they do, a reader holding an unverifiable certificate can do little more than notice that it is unverifiable — which is itself worth knowing.
This page explains a document. It is not advice about purchasing, preparing or using any product, and the compounds such documents accompany are sold for research use only and are not approved for human use.