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How to verify peptide purity with HPLC and mass spectrometry.

Every legitimate research peptide Certificate of Analysis is built on two analytical methods: reverse-phase HPLC with UV detection, which measures purity; and electrospray-ionisation mass spectrometry, which confirms identity. This guide explains what each method actually does, the standard conditions used worldwide, and how to verify a UK Peptides lot independently at any analytical laboratory.

See real HPLC + MS reports →Read the CoA guide

Method 1 of 2

RP-HPLC-UV: purity

Reverse-phase High-Performance Liquid Chromatography with UV detection separates the peptide from synthesis impurities: truncations, deletions, oxidation products, capping artefacts. The peptide is dissolved, injected onto a C18 column, and eluted under a polar-organic gradient. The detector records UV absorbance at 214 nm against retention time, producing the chromatogram printed on every legitimate CoA.

Purity is the area under the main peak expressed as a percentage of the area under every detected peak. UK Peptides applies a 99% floor to every lot before release.

Method 2 of 2

ESI-MS: identity

Electrospray Ionisation Mass Spectrometry confirms that the dominant compound in the vial is the molecule on the label. The peptide solution is sprayed through a charged capillary, the solvent evaporates, and gas-phase ions are accelerated into a mass analyser. The observed mass-to-charge ratio of the molecular ion is compared to the theoretical mass calculated from the peptide's primary sequence.

A match within ±0.1% confirms identity. Larger discrepancies indicate a sequence error, an unexpected modification, or contamination, any of which result in immediate rejection of the lot at UK Peptides.

HPLC method, in detail

Standard conditions for reverse-phase peptide HPLC.

The HPLC conditions below are the de facto standard used by independent testing laboratories and most academic analytical chemistry departments worldwide. When you see different numbers on a CoA, ask why. A reputable lab will explain.

Column
ZORBAX SB-C18 or equivalent · 4.6 × 150 mm · 3–5 µm particle
Mobile phase A
0.1% trifluoroacetic acid in water (HPLC grade)
Mobile phase B
0.1% trifluoroacetic acid in acetonitrile (HPLC grade)
Gradient
5–10% B to 70–90% B over 20–40 minutes
Flow rate
1.0 mL / min
Detection
UV at 214 nm (peptide bond), 280 nm secondary if needed
Column temperature
30–40 °C (controlled oven)
Injection volume
10–20 µL of 1 mg/mL peptide solution
Reported as
Area-under-curve % of main peak vs total detected peaks
Mass spec, in detail

How ESI-MS confirms peptide identity in five seconds.

Once the HPLC step has separated the peptide from impurities, mass spectrometry answers a single question: is the main peak the right molecule? Electrospray ionisation produces an intact molecular ion (no fragmentation), the mass analyser measures its mass-to-charge ratio, and the result is compared to the theoretical mass calculated from the peptide sequence on the label.

The example below uses BPC-157 (sequence GEPPPGKPADDAGLV, theoretical monoisotopic mass 1,419.55 Da). A reported observed mass of 1,419.54 Da on an ESI-MS spectrum is a clean identity match within standard tolerance, and is what appears on every Independent certificate for a UK Peptides BPC-157 lot.

Ionisation source
Electrospray (ESI), positive ion mode (ESI+)
Sample prep
Direct infusion or post-HPLC injection at 1–10 µg/mL
Solvent
50:50 acetonitrile / water + 0.1% formic acid
Mass analyser
Time-of-flight (TOF), quadrupole or Orbitrap
Reported as
Observed m/z vs theoretical monoisotopic mass
Tolerance
±0.1% mass error (high-resolution: ±5 ppm)
Example: BPC-157
Theoretical 1,418.70 Da · observed 1,418.59 Da (monoisotopic) · matched
Example: Retatrutide
Expected 4,731.3 Da · observed 4,731.2 Da (average, 20mg lot) · matched
Failure mode
Mismatch → lot rejected and destroyed
Independent verification workflow

How to re-test a UK Peptides lot yourself in five steps.

  1. 01

    Sample prep

    Dissolve ~1 mg of the lyophilised peptide in 1 mL HPLC-grade water (or a 50:50 water / acetonitrile mix for hydrophobic peptides).

  2. 02

    Run HPLC-UV

    Inject 10–20 µL onto a C18 column under a 0.1% TFA / acetonitrile gradient with detection at 214 nm.

  3. 03

    Calculate purity

    Express the area under the main peak as a percentage of the total area under all detected peaks. Compare to the figure on the supplied CoA.

  4. 04

    Run ESI-MS

    Inject the same sample into an ESI mass spectrometer in positive ion mode. Record the molecular ion m/z.

  5. 05

    Compare identity

    Compare observed mass to the theoretical mass of the named peptide. Match within ±0.1% confirms identity.

Multiple UK research labs have run exactly this workflow on UK Peptides lots and published the comparisons. See the case study on the high-purity peptides page for in-house re-test figures alongside the supplied CoA values.

Apply this to your next order

Products with verifiable HPLC and MS data.

Retatrutide 20mg

Triple-agonist · 4,731.3 Da average · ≥99% HPLC

View signed CoA →

BPC-157 5mg

Pentadecapeptide · 1,419.55 Da · ≥99% HPLC verified

View signed CoA →

TB-500 5mg

Thymosin Beta-4 analogue · 4,963.4 Da average · ≥99% HPLC

View signed CoA →

GHK-Cu 100mg

Copper tripeptide · 402.92 Da · ≥99% HPLC verified

View signed CoA →

FAQ

HPLC, mass spectrometry & peptide verification: questions answered.

Why are HPLC and mass spectrometry the standard for peptide verification?

HPLC and mass spectrometry answer two different questions about a peptide lot. HPLC-UV measures purity: how much of the material in the vial is the intended compound versus everything else. ESI mass spectrometry confirms identity: that the dominant compound is actually the named peptide. Neither method alone is sufficient; together they form the analytical floor for research-grade peptide characterisation worldwide.

What HPLC column is used to test research peptides?

Reverse-phase HPLC of peptides is almost universally run on a C18 (octadecylsilane-bonded) column, typically 4.6 mm internal diameter, 150 mm length, with 3–5 µm particle size and 100–300 Å pore size. C18 is the default because peptides are well-resolved on it under a polar-organic gradient, and the column chemistry is stable, well-understood, and reproducible across laboratories.

What mobile phase is standard for peptide HPLC?

A binary gradient of 0.1% trifluoroacetic acid (TFA) in water as solvent A, and 0.1% TFA in acetonitrile as solvent B. The gradient typically runs from 5–10% B up to 70–90% B over 20–40 minutes at a flow rate of 1.0 mL/min. TFA acts as an ion-pairing agent that sharpens peptide peak shape; acetonitrile elutes more hydrophobic peptides at higher concentrations.

What detection wavelength is used?

UV detection at 214 nm is the standard for peptide HPLC because the peptide bond absorbs strongly at this wavelength, making it sensitive to almost every peptide regardless of side-chain composition. Some labs use 220 nm as a secondary wavelength to reduce solvent baseline drift. 280 nm is used selectively for peptides containing tryptophan, tyrosine or phenylalanine residues.

What ionisation source is used for peptide mass spectrometry?

Electrospray ionisation (ESI), typically in positive ion mode (ESI+). ESI is a soft ionisation technique that produces intact molecular ions of peptides without fragmenting the peptide backbone, which makes it ideal for confirming molecular weight. The peptide solution is sprayed through a charged capillary, the solvent evaporates, and the resulting gas-phase ions are accelerated into the mass analyser.

How is observed mass compared to theoretical mass?

The theoretical monoisotopic mass of a peptide is calculated from its primary sequence using standard amino acid residue masses plus the masses of the terminal modifications. The observed mass from ESI-MS is compared to this calculated value; matches within ±0.1% are accepted as confirming identity. Larger discrepancies indicate a sequence error, a modification, or contamination.

Can I run these tests on my own samples?

Yes. Any analytical laboratory equipped with an HPLC-UV system and an ESI mass spectrometer can run peptide purity and identity. UK and EU researchers commonly use accredited analytical laboratories for independent verification. Re-testing a sample of a supplied lot is the gold standard for confirming a supplier's CoA.

Ready to apply this?

Every product page with a published lab report links the signed third-party CoA (HPLC chromatogram, ESI-MS identity confirmation, and the testing laboratory's signature) for the lot you would receive.

Browse verified peptides →See UK Peptides methodology