Measuring mass
Mass spectrometry measures the mass of molecules in a sample. Because a peptide’s mass follows from its sequence, comparing the measured mass with the expected mass helps confirm that the material is the intended molecule.
Identity vs purity
It is useful to separate two ideas: identity (is this the right molecule?) and purity (how much of the sample is that molecule?). Mass spectrometry speaks mainly to identity, while a method such as HPLC speaks to purity. A COA often reports both.
Reading it on documentation
On a certificate, an identity confirmation by mass spectrometry is a statement that the measured mass is consistent with the expected molecule for that batch. As always, the document describes the batch it names.
Frequently asked questions
Does mass spectrometry measure purity?
It primarily confirms identity by mass; purity is usually reported from a separate method.
What is being compared?
The measured mass of the material against the mass expected from its sequence.