Verification
What a complete certificate contains, how purity is measured, and what “third-party tested” does not mean.
Reading a certificate of analysis starts with the question most people skip: does this document name the lot in front of you. A complete certificate identifies a specific batch, states the analytical method used, names the laboratory, carries a date and a signature, and reports purity and identity as two separate results. A document missing any of those is not a weaker certificate, it is a different kind of object, and most of the ones circulating in this market are missing several.
Purity and identity are the pair that matters. Purity usually comes from reversed-phase HPLC, which separates a sample by how strongly its components bind to a column and reports each peak as a percentage of the total detected signal. That makes it a relative measure, not an absolute one, and it is blind to anything the detector cannot see. Identity comes from mass spectrometry, which measures molecular mass and confirms the main peak is the molecule it is supposed to be. A purity number on its own tells you a sample is mostly one thing, not which thing.
“Third-party tested” is the phrase doing the heaviest lifting in this market, and it has no fixed meaning. It can describe an independent laboratory testing a randomly drawn lot to a stated method, or a single test of a single batch years ago, or nothing at all. The question that deflates it is short and specific, and it is the subject of one of the editorials below.
Common questions
How do you read a certificate of analysis?
Check six things in order: does it name the specific lot you hold, does it name the testing laboratory, does it state the analytical method, is it dated and signed, does it report purity, and does it report identity separately from purity. A certificate that fails any of these cannot be verified against the vial in front of you, whatever number it prints.
How is peptide purity tested?
Purity is usually measured by reversed-phase high-performance liquid chromatography. A sample is pushed through a column that separates components by how strongly they bind to it, a detector records what comes off and when, and each peak is reported as a percentage of the total detected signal. The result is a relative purity figure for what the detector could see.
How does an HPLC purity test work, and what can it not show?
HPLC separates a mixture by differential binding to a column and reports the relative size of each peak. Structurally, it cannot tell you what a peak is, only that something eluted at a given time, and it cannot see anything the detector does not respond to. That is why identity confirmation by mass spectrometry is a separate test and not an optional extra.
What is a peptide test, and what does it establish?
In practice a peptide test means two analyses: HPLC for purity and mass spectrometry for identity. Together they establish that a sample is mostly one compound and that the main component has the expected molecular mass. They do not establish sterility, endotoxin levels, correct fill weight, or that the vial you received is the one that was tested.
What does “third-party tested” actually mean?
By itself, nothing fixed. The phrase has no standard definition, no required scope and no required frequency, so it covers everything from independent testing of a randomly selected lot to one test of one batch at an unspecified date. The deflating question is which lot, tested by whom, to what method, and can the document be matched to the vial in hand.
Does a high purity number mean the compound is what the label says?
No. Purity and identity are different measurements. A 99 percent purity figure means the detected signal was dominated by one component. It does not say which component, which is why a purity result without a matching identity result, from the same lot, leaves the most important question unanswered.
Read the evidence
6 pieces on this subject, every finding attributed and every gap stated.
Related topics
For research use only · Not for human or veterinary use · No compound discussed here is FDA-approved for any indication