Reading a certificate of analysis
What a lot number has to line up with, what each line on a certificate is actually measuring, and which labs turn up in the data we collect.
The eight lines we score
What is in the vial
We expect all three of these before we take a listing seriously.
- Identification
- Net content
- Net purity
What should not be
We score each one the vendor chooses to publish, and Conformity covers the batch rather than the vial.
- Endotoxins
- Sterility
- Heavy metals
- Fentanyl
- Conformity
The number that ties it all together
A listing only means something here if the vendor puts a lot or batch number on the product and that same number appears on a certificate for the same material. Where the two do not match, the certificate is about somebody else's vial.
- Certificate of analysis
- A lab's report on one sampled batch: what was tested, by what method, what came back, and what would have counted as a pass.
- Lot number
- The code tying a specific production run to that report. The vial, the box, and the certificate should all carry the same one.
Line by line
Identification
We expect this on every listing- What it proves
- The vial holds the compound named on the label.
- What it does not
- Says nothing about how much is in there, or how clean it is.
- How it is read
- Mass spectrometry, usually after a chromatographic separation. The instrument weighs the fragments, and the pattern either matches the labelled sequence or it does not. On a certificate this shows up as a pass beside a method name. Everything else on the sheet is moot if this line fails.
Net Content
We expect this on every listing- What it proves
- How much peptide the vial actually holds, against what the label claims.
- What it does not
- A vial can hit its stated mass and still be full of the wrong material — that is what identification is for.
- How it is read
- Peptides usually ship as a salt, and the counterion weighs something. A gross figure counts that salt; a net figure does not, so read which one you are being shown before comparing two vendors. Measured by HPLC against a certified reference standard and reported as a percentage of the label claim.
Net Purity
We expect this on every listing- What it proves
- How much of what is in the vial is the compound you wanted, rather than truncated chains, oxidised residues, or leftover reagent.
- What it does not
- A high figure is about chemistry, not safety — it does not rule out bacteria, endotoxin, or metals.
- How it is read
- HPLC. The chromatogram is integrated and the target's peak is expressed against the total peak area, so the number is a share of what the detector saw and not of the whole vial.
Endotoxins
Scored when a vendor publishes it- What it proves
- Whether the batch carries the cell-wall fragments left behind by Gram-negative bacteria.
- What it does not
- Does not tell you anything is alive in there, and does not cover other contaminants.
- How it is read
- The LAL assay, reported in EU per mg or per mL. Worth knowing that a batch can be perfectly sterile and still fail this, because the bacteria that shed the fragments do not have to survive.
Sterility
Scored when a vendor publishes it- What it proves
- That nothing viable was growing in the sample — no bacteria, yeast, or mould.
- What it does not
- A clean result here says nothing about endotoxin, which is a separate line on the sheet.
- How it is read
- The sample is either inoculated into growth media directly or filtered onto a membrane, then incubated and watched. A pass means nothing grew under those conditions.
Heavy Metals
Scored when a vendor publishes it- What it proves
- Whether elemental contaminants — lead, arsenic, cadmium, mercury and their neighbours — came along from the reagents, raw materials, or the equipment.
- What it does not
- Screens for elements, so it will not surface an organic impurity of any kind.
- How it is read
- ICP-MS, which reaches parts-per-billion. Certificates normally print a limit beside each element rather than a single overall verdict.
Fentanyl
Scored when a vendor publishes it- What it proves
- That the batch was checked for fentanyl and its close structural relatives.
- What it does not
- It is a targeted screen, so it only finds what it was told to look for.
- How it is read
- LC-MS/MS at trace detection limits. This sits outside the usual identity and purity panel, so a vendor has to commission and publish it deliberately for it to appear at all.
Conformity
Scored when a vendor publishes it- What it proves
- That several vials pulled from one lot agree with each other.
- What it does not
- It is a batch-level check, so it can never speak for the specific vial you were sent.
- How it is read
- Identity, content, and purity re-run across multiple pulls from the same run. This is the only line that can surface uneven filling or contamination confined to part of a batch — a single-vial certificate cannot.
Labs that show up in our data
Each of these appears on at least one certificate we have collected. Listing one is a statement of fact about our data, not a recommendation — and accreditation, where we mention it, is the lab's own claim rather than something we have audited.
ILS Labs
ISO 17025 accredited, based in San Diego. Runs full peptide QC panels and puts a QR code on its certificates so you can verify one.
Vanguard
ISO/IEC 17025 accredited. Covers identity, HPLC purity, endotoxin, sterility, and metals by ICP-MS.
Ethos Analytics
ISO 17025 accredited lab in Phoenix. Peptide quantitation alongside nutraceutical, food, and OTC work.
Eagle Analytics
Analytical chemistry and microbiology aimed at FDA-regulated clients.
MZ Biolabs
Tucson-based, built around mass spectrometry for research and medical customers.
Janoshik
Widely used for peptide and small-molecule analysis; certificates turn up across a lot of vendors.
Freedom Diagnostics
Purity work on research-use peptides, with certificates searchable online.
Chromate
US supplement analysis. Results are published through its own verification portal.
Kovera Labs
Compound testing with a certificate-verification service.
AFI
Analytical Formulations Lab. General analytical scope rather than a peptide specialism.
How old is too old
A certificate describes one batch on one day, so age matters. Where we know the date, we show it and let you weigh it — we do not drop a listing for having an older certificate, and we would rather show you the date than quietly decide for you. A vendor who republishes results as batches turn over is telling you something a vendor sitting on a two-year-old sheet is not.
Educational only, and not medical advice. Where our summary and the lab's report disagree, the report wins. We aggregate what retailers choose to publish; we do not audit certificates.