Mass Spectrometry

Also known as: MS · mass spec

Mass spectrometry (MS) is a lab method that measures the mass of molecules, used to confirm a peptide is the molecule it is supposed to be.

Mass spectrometry turns molecules into charged particles (ions) and measures their mass-to-charge ratio. For a peptide, the result can be compared with the mass expected from its amino-acid sequence. If the measured mass matches, that is evidence the main component is the intended molecule; if it does not, something is different, such as a missing or extra amino acid or an altered end group. Tandem MS goes further by breaking the peptide into fragments, which can confirm the sequence itself.

MS is usually coupled to liquid chromatography (LC-MS). The chromatography separates the components and the mass spectrometer identifies each one. That is why HPLC and MS show up together on a complete COA: HPLC measures how much of the sample is the main peak, and MS shows what that peak is.

Why it matters

Purity without identity is an incomplete answer. A vial can contain one dominant compound that is not the one on the label, and an HPLC-only report cannot rule that out. Labs that analyze illegal peptide products use MS for identification for this reason.

MS can also catch small structural problems. In one confiscated product, high-resolution LC-MS identified a modified growth hormone-releasing hormone analog and showed that part of it lacked a C-terminal amidation that the intended molecule should carry, a sign of poor manufacturing quality. Reviews of peptide medicines list many such related impurities, including deletion and insertion sequences, which MS is suited to detect. Substituting a cheaper peptide, or shipping a related sequence, could leave an HPLC purity number looking normal while the measured mass would not match.

How to read an MS result on a COA

Find the expected (theoretical) mass for the peptide and the observed mass reported by the lab.
Check that they agree. Labs often report the mass of charged forms, so the report should state which ion was measured.
Confirm the MS result is for the same batch and date as the HPLC purity result.
If only a statement such as 'identity confirmed' appears with no numbers or spectrum, ask the lab or seller for the data.

m/z = (molecular mass + number of added protons × 1.007) ÷ charge

Worked example

A peptide with an expected mass of 1,000 daltons measured as a doubly charged ion appears near m/z 501: (1,000 + 2 × 1.007) ÷ 2 = 1,002.014 ÷ 2 = 501.007. If a report shows a peak near 501 and calls it the 2+ ion, that is consistent with the expected mass.

Common mistakes

Accepting a COA with HPLC purity but no identity test.
Accepting 'identity: conforms' with no expected mass, observed mass or spectrum.
Assuming an MS match proves purity; MS confirms what the main component is, while HPLC measures how much of the sample it makes up.
Assuming an MS result for one batch applies to later batches.
Assuming MS testing covers sterility or endotoxin, which need separate tests.

Sources

ReferenceAnalysis of illegal peptide drugs via HILIC-DAD-MS. Talanta, 2017. PMID 28738623.
ReferenceIdentification of the growth hormone-releasing hormone analogue [Pro1, Val14]-hGHRH with an incomplete C-term amidation in a confiscated product. Drug Test Anal, 2014. PMID 25283153.
ReviewRelated impurities in peptide medicines. J Pharm Biomed Anal, 2014. PMID 25044089.

Page updated October 3, 2026. How we grade evidence: methodology.

Related Terms

HPLC (High-Performance Liquid Chromatography)

HPLC (high-performance liquid chromatography) is a lab method that separates a sample into its components so the main compound's purity can be measured.

COA (Certificate of Analysis)

A certificate of analysis (COA) is a lab report showing test results, such as purity and identity, for one specific production batch of a product.

Vendor Trust Score

DoseCraft's vendor trust score is an editorial rating of a peptide seller's documentation, testing claims, reputation and business details, not a lab result.

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