Mass spectrometry identity

An identity check that measures a molecule's mass and compares it with the value calculated from the intended sequence — answering whether the right molecule is present, not how much of it there is.

Mass spectrometry ionises a sample and measures the mass-to-charge ratio of the resulting ions. For a peptide, the observed mass is compared against the theoretical value calculated from its amino-acid sequence. A match within the instrument's stated tolerance is consistent with the intended molecule; a substantially different mass is not, however clean the chromatogram looks.

Identity and purity answer different questions, and a certificate needs both. Chromatography reports how much of what was detected is one compound but cannot by itself say which compound that is; mass spectrometry says whether the molecule is the right one but not what fraction of the sample it makes up. A report carrying an HPLC figure with no identity confirmation leaves open the possibility of a clean trace of the wrong substance.

Small differences between observed and theoretical mass arise routinely from instrument mass accuracy and from which isotopic peak is reported, which is why reports state a tolerance. Certificates published on this site carry the observed and theoretical values side by side so the comparison can be read directly.

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.