Laboratory quality
LC-MS
Liquid chromatography–mass spectrometry — how peptide identity is confirmed and what its typical CoA line actually verifies.
- Last updated:
- 2026-07-22
Overview
Liquid Chromatography–Mass Spectrometry (LC-MS) couples an HPLC-style separation to a mass spectrometer that measures the mass-to-charge ratio of ionised molecules. For a peptide, the result is a mass spectrum that shows the peptide's molecular mass with high precision.
On a CoA, LC-MS is typically used for identity confirmation: the observed mass is compared to the theoretical mass calculated from the peptide's sequence.
Why it matters
LC-MS is what turns "we think this is peptide X" into "the mass observed is consistent with peptide X within measurement tolerance." It is the most direct laboratory answer to "is this actually the molecule the label says?"
Key concepts
Theoretical vs. observed mass
The peptide's sequence determines a theoretical monoisotopic mass. LC-MS measures the observed mass. A well-drafted CoA reports both and shows that the two agree within instrumental tolerance.
Charge states
Peptides are often observed as multiply charged ions ([M+H]+, [M+2H]2+, etc.). The mass spectrometer reports mass-to-charge; the analyst deconvolves to the true mass.
Sensitivity to structural changes
Even small structural changes (deamidation, oxidation) shift the mass by a predictable amount and are often detectable on LC-MS.
Common misconceptions
- "Correct mass" is not the same as "correct sequence." Two different amino-acid orderings with the same composition can have the same mass. For most therapeutic peptides that is not a real ambiguity, but for de novo identification it matters.
- LC-MS does not quantify potency by itself. It reports what molecule is present, not how much biological activity it has.
- LC-MS does not measure sterility or endotoxin.
Practical interpretation
When a CoA line reads "identity confirmed by LC-MS" with a specific observed mass, it is direct evidence that the molecule tested is the expected peptide. It is not evidence that every vial from the batch is what the label says; it is evidence about the specific sample the lab tested.
Limitations
Sample handling affects results. A CoA is only as good as the chain of custody between the batch and the tested sample.