Does 99% purity mean 99% of the vial is peptide?

No. It means 99% of what the detector saw. Salts, water and residual solvents that do not absorb at the monitored wavelength are invisible to the measurement.

Why 214 nm rather than 280 nm?

The peptide bond absorbs at 214–220 nm, so every peptide is detected. 280 nm relies on aromatic residues, which many peptides lack.

Can HPLC confirm identity?

Only weakly. Retention time depends on the exact instrument and method. Mass spectrometry establishes identity.

What HPLC Testing Actually Measures

The short answer

Reverse-phase HPLC separates peptides by hydrophobicity and reports purity as the target peak's share of total peak area. That figure is only as complete as what the detector sees. Anything not absorbing at the monitored wavelength is invisible to it.

Key facts

Technique: Reverse-phase HPLC
Separates by: Hydrophobicity
Typical detection: UV at 214–220 nm
Purity expressed as: Area percent of total
Blind to: Anything not absorbing at that wavelength
Invisible to it: Salts, residual solvents, water

How the separation works

The column packing is hydrophobic. A sample is loaded in a mostly aqueous mobile phase, where hydrophobic molecules stick to the packing, then an increasing gradient of organic solvent (usually acetonitrile) progressively releases them. More hydrophobic species elute later. Compounds differing slightly in sequence usually differ slightly in hydrophobicity, which is what makes the separation useful.

What the detector actually sees

Most peptide HPLC monitors ultraviolet absorbance around 214 to 220 nm, where the peptide bond itself absorbs. That is deliberate: it detects any peptide regardless of whether it contains aromatic residues, which 280 nm cannot. The trade-off is that many other things absorb there too, including some solvents.

Research material referenced

BPC-157 5mg, third-party HPLC tested

Buy BPC-157 · £15.99

The limitation that matters most

Area-percent purity is a ratio of what the detector sees. Anything that does not absorb at the monitored wavelength contributes nothing to the total and is therefore invisible. It cannot reduce the purity figure no matter how much is present. Inorganic salts, water and some counter-ions fall into this category. A 99% figure describes 99% of the detectable material, not 99% of what is in the vial.

Why the chromatogram matters more than the number

A single number hides the shape of the result. A trace with one sharp peak and a flat baseline is a different result from one with a main peak and several small shoulders summing to the same percentage. Shoulders close to the main peak often indicate deletion sequences or oxidised species, which are the impurities most likely to matter. A purity figure without a chromatogram is an assertion; with one it is a measurement you can check.

What HPLC does not establish

Identity. A pure sample of the wrong compound gives a beautiful chromatogram. Retention time is weak evidence of identity because it depends on the exact column, gradient and instrument, so it is comparable only against a standard run under identical conditions. Mass spectrometry is what confirms identity, and the two analyses answer different questions.

Reading a figure in context

Expected purity depends on the synthesis. A five-residue peptide should be very pure; a thirty-residue one with difficult couplings has more scope for deletion sequences and a lower figure is less alarming. Judging a number without knowing the length and composition of what was made gives it more or less weight than it deserves.

Frequently asked questions

Does 99% purity mean 99% of the vial is peptide?: No. It means 99% of what the detector saw. Salts, water and residual solvents that do not absorb at the monitored wavelength are invisible to the measurement.
Why 214 nm rather than 280 nm?: The peptide bond absorbs at 214–220 nm, so every peptide is detected. 280 nm relies on aromatic residues, which many peptides lack.
Can HPLC confirm identity?: Only weakly. Retention time depends on the exact instrument and method. Mass spectrometry establishes identity.

Extended research context

The Peptide Reference deep dive

Deep dive: what 'peptide' actually means

A peptide is a short chain of amino acids linked by peptide bonds, typically 2–50 residues. Above that boundary the molecule is usually called a protein. Peptides can be endogenous (produced by the body) or synthetic (manufactured by solid-phase peptide synthesis, SPPS). The 'research peptide' category refers specifically to synthetic peptides supplied for laboratory use: not medicines, not supplements.

Why HPLC and mass spec together

HPLC (High-Performance Liquid Chromatography) reports the purity of a batch by measuring what percentage of the sample matches the target peptide's retention time. Mass spectrometry independently confirms the target's molecular weight. Together they answer two different questions: 'is it clean?' and 'is it the right molecule?'. A CoA that reports only one is incomplete.

How to read a Certificate of Analysis

A complete peptide CoA lists: batch number, HPLC purity (area %), mass-spec measured mass vs theoretical, water content (Karl Fischer), acetate/counterion content, appearance, and often endotoxin and residual solvents. Learn to spot the missing fields, as that's usually where quality claims fall apart.

Research applications

▸Reference standards for analytical method development
▸Comparator peptides in receptor-binding assays
▸Stability testing of lyophilised material
▸Formulation R&D for topical and aqueous carriers
▸Teaching material for peptide chemistry courses

Handling checklist

✓Confirm HPLC ≥98% and mass-spec identity on CoA
✓Store lyophilised at −20 °C long-term
✓Reconstitute with bacteriostatic or sterile water only
✓Aliquot to minimise freeze/thaw cycles
✓Label vials with date, concentration, and batch

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Buying a peptide without a CoA

Fix: Insist on an in-batch HPLC + mass-spec certificate before purchase.

✗ Using DI water for reconstitution

Fix: Use bacteriostatic (0.9% benzyl alcohol) or sterile water only.

✗ Storing lyophilised vials at room temperature long-term

Fix: Freeze at −20 °C; short-term 2–8 °C is acceptable for weeks, not months.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

UKP

Written and reviewed by

The UK Peptides Editorial Team · Research library, UK Peptides

The editorial team is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate. Corrections are made in place and the review date updated.

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HPLC Testing for Peptides