Is it actually the peptide on the label?

How it works

1. 01
   Dissolve and separate

   A few micrograms are dissolved and run through a reversed-phase column so the peptide reaches the detector apart from salts and impurities.
2. 02
   Ionize

   Electrospray puts charge on the molecule. Peptides pick up several protons, so one peptide shows up at several m/z values: [M+2H]²⁺, [M+3H]³⁺ and so on.
3. 03
   Measure and deconvolute

   The instrument records each m/z to a fraction of a Dalton. We read the charge state from the spacing of the isotope peaks and compute the neutral mass. For BPC-157, [M+2H]²⁺ at 710.8 gives 1419.5 Da.
4. 04
   Confirm the sequence

   The ion is fragmented and the fragment ladder is matched to the expected sequence. Two peptides can share a mass; they rarely share a fragment pattern.

What the result means — and what it doesn't

Match means the measured mass agrees with the expected mass within tolerance and the fragment pattern fits the sequence. Mismatch means it does not — the result names the closest known peptide when there is one (a semaglutide vial that measures as liraglutide, for instance). Identity says nothing about how much is there or how pure it is; those are separate tests on the same page.

Why another lab might report a different number

• Monoisotopic versus average mass: the two differ by about 1 Da for a 1,400 Da peptide. We report which we used.
• Charge-state misassignment turns a correct [M+2H]²⁺ into a wrong mass. We print the observed m/z and charge so the arithmetic is checkable.
• Salt adducts (TFA, acetate, sodium) shift peaks. Our tolerance window and adduct handling are stated on the result.
• Mass alone cannot separate isomers or some analogs; a lab that skips fragmentation may call a match where we would not.

That's why every result here prints the method and the limit next to the number. The full science article on why tests vary.