The role of mass spectrometry in purity verification
Tide Front Supply Research Team · Apr 4, 2026 · 1 min read
Why HPLC purity numbers alone don't prove identity, and how MS data close the loop.
HPLC tells you a sample is clean. Mass spectrometry tells you it's the right thing. Both matter; neither replaces the other.
What MS measures
A peptide's molecular weight is determined by its amino-acid composition. ESI-MS or MALDI-TOF can measure that weight to within a fraction of a Dalton, distinguishing the target sequence from common synthesis byproducts.
Common confounders
- Truncated sequences: missed couplings during synthesis can produce peptides one or two residues short.
- Oxidation: methionine and tryptophan oxidize during synthesis or storage, shifting mass by +16 Da per event.
- Deamidation: asparagine and glutamine convert to aspartate and glutamate over time, shifting mass by +1 Da.
What we report
Every CoA includes the observed mass and the theoretical mass. A delta of less than 1 Da on a peptide under 5 kDa is normal instrument tolerance; a delta of 16 Da means oxidation; a delta of -114 Da means a missing amino acid.
If those numbers don't match what's claimed, don't run the experiment.