What the method does
Liquid chromatography separates a mixture over time; mass spectrometry measures the mass‑to‑charge ratio of what comes off. A peptide has a calculable molecular mass, so a peak at the expected mass confirms the molecule is what the label says.
That is a genuinely strong claim, and it is the claim most worth having. Substitution and mislabeling are real failure modes in this category, and identity testing is what catches them.
Where its authority ends
| Question | Answered by LC-MS? | What answers it |
|---|---|---|
| Is this the right molecule? | Yes | LC-MS |
| What fraction is the target? | Partly | HPLC-UV purity |
| How much is in the vial? | No | Net content, measured fill |
| Are there pyrogens? | No | USP <85> endotoxin, LAL |
| Is there microbial contamination? | No | PCR screen, or USP <71> for sterility |
| Is it sterile? | No | USP <71>, roughly fourteen days |
| Is the vial on my shelf still good? | No | Nothing. Testing characterizes a sample at a point in time. |
Why the distinction matters commercially
A supplier who implies a purity certificate covers sterility is either confused or hoping the buyer is. It is the single worst claim to overstate on an injectable‑format product, and it is the kind of overstatement that regulators and underwriters both treat seriously.
The honest strong version
A five‑measure panel — identity, purity, net content, endotoxin and microbial screening,
run by an independent laboratory — is a substantial claim without touching sterility. Four of
those five go beyond a purity number, which is more than most of this category can document.