Every UK research peptide supplier prints a purity figure. Most print 99%, some 98%, a few claim 99.9%. The number is meaningful only if you know how it was produced, what it is a percentage of, and what it leaves out. This article explains the method behind the figure so that “99% HPLC purity” reads as a measurement rather than a slogan.
The method in one paragraph
High-performance liquid chromatography dissolves a small amount of the sample and pumps it, under pressure, through a column packed with fine particles. Different molecules interact with the packing differently and emerge from the column at different times, called retention times. A detector at the outlet, usually ultraviolet absorbance at around 214 or 220 nm where the peptide bond absorbs, records a signal as each component passes. The result is a chromatogram: signal against time, with a peak for each component.
What the percentage is
Purity by HPLC is area-percent: the area under the main peak divided by the total area under all peaks, times one hundred. If the main peak has 99.2% of the total area, purity is reported as 99.2%.
That definition has consequences.
It is a percentage of what the detector sees, not of the vial’s mass. Water, counter-ions such as acetate or trifluoroacetate, and inorganic salts do not absorb at the detection wavelength and are invisible to the test. A powder that is 99% pure by HPLC may be 80% peptide by weight, with the remainder being water and counter-ion. That second figure is called peptide content or net peptide and is a separate test.
It counts related substances, not everything. The minor peaks are almost always related to the main compound: sequences missing an amino acid (deletion sequences), sequences that stopped short (truncations), oxidised methionine or tryptophan variants, and residual protecting groups from synthesis. These are what the other one percent usually is.
It depends on the method. A gradient that resolves impurities well will show a lower purity than a fast gradient that lets small peaks hide under the main one. This is why a certificate should state the method and show the chromatogram.
Why purity alone proves nothing about identity
A purity test measures how much of the sample is one compound. It does not say which compound. A vial of the wrong peptide, or of a similar but cheaper sequence, can score 99% purity by HPLC and be entirely mislabelled.
Identity is a separate test, done by mass spectrometry. The instrument measures the molecular weight of the main component and compares it with the theoretical molecular weight of the labelled compound. For BPC-157 that is about 1,419.5 g/mol; for GHK-Cu about 403.9; for LP3-R about 4,731.5. A match confirms identity. A purity figure without an identity result should be read as “this vial is 99% something”.
Every BluePeak certificate reports both, and Janoshik’s verification page shows both.
How to compare purity claims between suppliers
- Is there a certificate for the specific lot? A figure on a website with no lot-specific document behind it is marketing.
- Who did the test? In-house testing is not independent. Look for a named third-party laboratory and a test number that can be checked on that laboratory’s own site.
- Is the chromatogram shown? Area-percent is only credible with the trace it was calculated from.
- Is identity reported? Mass spectrometry, or at minimum a molecular weight result.
- Is the client on the certificate the supplier you are buying from? Certificates are sometimes reused from other companies’ lots.
A 2026 survey of UK research-peptide vendors by an independent COA directory found that fewer than one in ten published their own verifiable Janoshik certificate; the rest showed none, borrowed or unverifiable documents. That is the market context for any purity claim.
What BluePeak’s specification is
Our release specification is 99% purity by HPLC, with identity confirmed by mass spectrometry, on every lot, tested by Janoshik Analytical. Lots that fail specification are rejected, not relabelled. The current published records are listed on the Certificates of Analysis page, each linked to its record on verify.janoshik.com.
Glossary of the terms used here
- Area-percent: the main peak’s share of total peak area on a chromatogram.
- Chromatogram: the trace of detector signal against time.
- Related substances: impurities structurally related to the main compound.
- Peptide content: the proportion of the powder’s mass that is peptide, as opposed to water and counter-ion.
- Identity: confirmation that the compound is what the label says, by mass spectrometry.
BluePeak Peptides supplies research peptides for laboratory use only. This article describes analytical methods and is not guidance for use.
