The testing lifecycle

What actually happens when a sample is tested

"Third-party tested" is two words. The work behind them is a sequence of separate tests, each answering a different question, ending in a signed document. Here is what each step measures and why it is on the report, in the order it happens.

1. A specific batch is sampled

   Testing describes one production lot, not a catalogue. A sample is drawn from a specific batch and sent to a named independent laboratory. Everything that follows ties back to that lot number, which is why the lot on the report should match the lot on the vial.

2. Identity, confirmed by mass spectrometry

   Mass spec measures the molecular mass of the compound and checks it against the expected mass for the named molecule, within a small tolerance. This is the test that confirms the sample is the molecule it claims to be. A high purity figure on the wrong molecule is still the wrong molecule, so identity comes first.

3. Purity, measured by HPLC

   High performance liquid chromatography separates the sample into its parts and measures the size of each. The result is the proportion of the material attributable to the target compound, shown as a chromatogram: one tall peak for the target and small peaks for everything else. The chart is the proof behind the figure.

4. Net peptide content, the number the category buries

   Purity is a proportion of what is in the vial, not a measure of how much compound is in the vial. Net peptide content reports the actual mass of peptide, separate from the bound water and salt. A sample can be highly pure and still hold far less compound than the label implies. A report that shows purity but not content has answered the easier question.

5. Endotoxin and sterility, where applicable

   Where contamination is a relevant quality measure for a batch, the lab runs endotoxin testing for bacterial byproducts and sterility testing for live microbial growth. Endotoxin is reported against a defined limit. Purity and identity describe the compound; these describe the conditions it was produced and handled in. A lab that documents them across batches is recording more of its process.

6. The signed certificate of analysis

   The lab compiles the results into a single signed document and issues it under its own name. The company does not write the result. What you should be able to obtain is a signed certificate of analysis from a named independent lab, carrying the chromatogram and the net peptide content, that you can confirm directly with the lab that issued it.

Why the order matters

Each step assumes the one before it. Purity assumes the molecule is correct, which only identity establishes. Content assumes there is a clean peptide fraction to weigh. Read top to bottom, the report is a chain of questions, each closing a gap the one before it left open. A document that skips a step has left that question open.

New here? Start with what a real COA shows, or browse the reference library.