Mass spectrometry (MS) is commonly used to check whether the measured molecular mass of a peptide agrees with its expected mass. It is an identity check—not a complete assessment of purity, content or biological activity.
What the test measures
The instrument ionizes molecules and separates the resulting ions according to mass-to-charge ratio. The laboratory interprets the spectrum and reports a measured molecular mass or characteristic ion pattern.
For a useful comparison, the expected structure must be clear. Amidation, acetylation, oxidation, counter-ions and other modifications can change the expected result.
What a conforming result means
A result that agrees with the theoretical molecular mass supports the presence of the intended peptide. The acceptable difference depends on the instrument, method and laboratory criteria; it should not be invented after the test.
- Expected molecular formula or sequence
- Theoretical molecular mass
- Observed molecular mass
- Instrument or method description
- A clear conclusion such as conforms or does not conform
What MS does not establish
Identity by MS does not by itself show how much peptide is in the vial, how pure the sample is, whether endotoxin is controlled, or whether the product is suitable for a particular use. Those questions require separate tests such as HPLC purity, quantitative content or endotoxin analysis.
Choosing the scope
For a basic research-peptide check, MS identity and HPLC purity are often requested together. Complex formulations, mixed peptides and unknown samples may need LC-MS or another project-specific approach. Confirm the sample form, expected analyte and reporting purpose with the laboratory before shipping.