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When do I need LC-MS for a peptide?
The short answer
When identity is the actual question rather than purity. Mass spectrometry measures molecular mass directly, so it distinguishes compounds that chromatography cannot separate — closely related analogues, fragments sold under the same market name, or an unexpected substitution. If you only want to know how clean and how much, HPLC with UV answers that on its own.
In detail
Concrete cases where it earns its cost: telling full-length thymosin β-4 from the short LKKTETQ fragment sold as the same product; separating CJC-1295 with and without the DAC linker; confirming which Semax variant a vial holds; and any first purchase from an unknown supplier where identity has never been established.
On our tariff it is a €79 add-on that adds five to seven days to turnaround.
It is also the correct escalation when a retention-time result looks anomalous and you want the question settled rather than repeated.
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