Home Blog Reading the paperwork
Reading the paperwork
Purity is not potency
HPLC, mass spectrometry and Karl Fischer each answer a different question. Three suppliers quoting "99%" may be quoting three different things.
Three numbers get used interchangeably in this market and they are not interchangeable. Knowing which one a supplier means is most of the work of comparing two of them.
| Assay | Question it answers | What it cannot tell you |
|---|---|---|
| RP-HPLC, 214 nm | What fraction of the peptide present is the one you wanted | How much peptide is present at all |
| Mass spectrometry | Is this the molecule you ordered | How much of it there is |
| Karl Fischer | How much water is in the solid | Anything about the peptide |
| Net peptide content | What fraction of the solid is peptide | Whether it is the right peptide |
The gap that matters
Purity is a ratio between peptides. Net content is a ratio between peptide and everything else in the vial. A sample can be 99 per cent pure and 74 per cent peptide simultaneously, and a supplier quoting the first number without the second is not lying — they are answering a question you did not ask.
Reading a chromatogram
At 214 nm the detector is reading the peptide bond, so it sees peptides and is close to blind to salt and water. One dominant peak with a flat baseline is what you want. Shoulders on the main peak usually mean deletion sequences that co-elute; a cluster of small peaks late in the run often means oxidation.
Every lot we release ships with its trace. The quality section of the home page shows one, and the figure on it is the peak area purity for that lot rather than a house average.
For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.