Mass spectrometry: the identity of a batch
HPLC shows how clean a sample is. Mass spectrometry shows whether it is the right molecule at all.
Mass spectrometry (MS) answers a simple but decisive question: is the molecule in the vial the molecule on the label?
How it works
For peptides, electrospray ionisation (ESI) is mostly used. The molecules are gently converted into charged ions without breaking down. The instrument then measures the mass-to-charge ratio, m/z for short.
Because peptides can accept several protons, the same molecule often appears multiple times in the spectrum:
| Ion | Meaning | Example BPC-157 (m/z) |
|---|---|---|
| [M+H]⁺ | singly protonated | approx. 1419.7 |
| [M+2H]²⁺ | doubly protonated | approx. 710.4 |
If the measured values match those calculated from the sequence, identity is confirmed.
Theory versus measurement
The sequence yields a theoretical mass. The deviation of the measurement from this is given in daltons or in ppm. How large it may be depends on the instrument: high-resolution systems achieve a few ppm, routine instruments are in the range of a tenth of a dalton.
LC-MS: both in one run
HPLC and MS are frequently coupled. This allows not only the main peak to be identified, but also every minor peak to be assigned a mass. This turns an anonymous impurity into a concrete finding, such as a missing amino acid or an oxidation.
Why both belong together
- HPLC without MS: clean, but possibly the wrong molecule
- MS without HPLC: the right molecule, but an unknown amount of accompanying substances
Only the combination provides a reliable picture. That is why every one of our batch reports contains both methods.