Reading time: ~2 min · Part of the free certification in peptide science
Purity without identity is not enough: you could have 99% of the wrong molecule. Mass spectrometry (MS) confirms identity by measuring molecular weight with high accuracy.
- Techniques: ESI-MS (electrospray ionization) and MALDI-TOF are the most used for peptides. They generate ions whose mass-to-charge ratio (m/z) allows the mass to be reconstructed.
- Observed vs. theoretical mass: identity is confirmed when the measured mass matches the calculated mass of the sequence. It is worth distinguishing monoisotopic mass (using the most abundant isotope of each element) from average mass (weighted mean of isotopes); in large peptides the difference is appreciable.
- Amino acid analysis (AAA): a complementary technique that hydrolyzes the peptide and quantifies its composition, corroborating the sequence and helping to determine peptide content.
Robust control combines both: MS says what it is (identity, from the mass) and HPLC says how pure it is (purity, from the peak area). A serious COA presents both, each with its graph: the mass spectrum and the chromatogram.
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