A chromatogram with one sharp peak proves a sample is pure — but pure what? A synthesis error can yield a highly pure wrong sequence. Mass spectrometry closes that gap by measuring the molecule's mass directly.
ESI vs MALDI
- Electrospray ionisation (ESI) produces multiply charged ions and pairs naturally with LC for LC-MS identity checks.
- MALDI-TOF ionises from a solid matrix and is fast for single-mass confirmation of larger peptides.
Reading the result
Compare the observed mass with the theoretical molecular weight calculated from the sequence. Agreement within instrument tolerance confirms identity; a mismatch of 18 Da can signal a missing water (cyclisation) and a mismatch equal to one residue can indicate a deletion sequence.
What a complete CoA should include
- Sequence or structure and theoretical molecular weight
- Observed mass from MS
- HPLC purity with chromatogram
- Lot number and analysis date
- Appearance and recommended storage
For the purity side of the story, see our guide to HPLC purity and the Certificate of Analysis.
