How to Read a Peptide Certificate of Analysis

A certificate of analysis is the only document that connects a numbered vial of research peptide to a measurement someone actually made. Everything else on a product page is a claim. The certificate is the evidence, and it is worth knowing how to read one before paying for the vial it describes.

This post walks through the two tests on almost every peptide report, HPLC purity and mass spectrometry identity, explains what 99% does and does not tell you, separates purity from net peptide content, and sets out what independent testing of online peptides has found.

What a certificate of analysis is, and who issues it

A certificate of analysis, usually shortened to CoA, is a batch-specific report from an analytical laboratory stating what was tested, by which method, on what date, and with what result. A report without a batch number is a brochure.

The lab may be the manufacturer's own quality department or an independent contract lab. Either way the report should name the method and show the chromatogram and mass spectrum, not just a summary line.

LynxLab publishes the lab reports for every batch on the product page itself, so the number on the vial and the number on the report can be matched before the seal is broken. A generic PDF shared across batches defeats the point of the document.

HPLC purity: what the main peak measures

High-performance liquid chromatography separates the contents of a sample by pushing it through a column under pressure. For peptides the workhorse is reversed-phase HPLC, in which molecules separate by hydrophobicity; it has been the standard tool for peptide purification and analysis for decades (Mant et al., Methods in Molecular Biology, 2007).

A detector, usually ultraviolet absorbance, records a trace as compounds leave the column. The target peptide produces the main peak. Anything else, truncated sequences, oxidised variants, leftover protecting groups, produces smaller peaks at other retention times.

The purity figure is the area of the main peak as a percentage of the total area of all peaks. One tall peak on a flat baseline is a clean batch; a forest of small peaks is not, whatever number is typed above it.

That is why a report should show the trace. The number alone can be copied; the chromatogram has to be produced. A peptides uk buyer who sees purity stated without a chromatogram has been shown a claim, not a result.

Mass spectrometry: identity is a separate question

HPLC tells you how clean a sample is, not what it is. A pure sample of the wrong peptide produces a perfect chromatogram.

Mass spectrometry answers the identity question by measuring the mass of the molecule. Therapeutic peptides generally fall between 500 and 5,000 daltons (Wang et al., Signal Transduction and Targeted Therapy, 2022), and each sequence has a calculable theoretical mass. The report should state the expected mass, the mass found, and the difference, which should be small.

The FDA's own laboratory has published on why this matters. Zhang and colleagues found that HPLC-UV methods submitted for peptide drugs "may be insufficient for ensuring the quality of peptide drug products", after identifying an amino acid deletion and an insertion in a synthetic peptide that the applicant's HPLC method could not resolve. Their high-resolution LC-MS method could detect an impurity present at less than 0.1% of the drug concentration and confirm the sequence in the same run (Zhang et al., AAPS Journal, 2015).

For a blend, identity has to be shown for each component. A single vial of cjc-1295 ipamorelin contains two peptides with two different masses, and a report that confirms one and assumes the other has done half the job.

What 99% means, and what it does not

A 99% HPLC purity figure tells you three things: the batch was tested, the main peak dominated the trace, and related impurities were under one per cent of the UV-absorbing material.

Three things it does not tell you: whether the main peak is the right molecule (that is mass spectrometry), how many milligrams of peptide are in the vial (that is net peptide content), and whether the vial is sterile or free of endotoxin (those are separate microbiological tests that most research-grade reports do not include).

The FDA's description of BPC-157, when it placed the peptide in category 2 of its compounding bulk substances list, is a useful reminder that purity and characterisation are hard problems. It cited "complexities with regard to peptide-related impurities and active pharmaceutical ingredient (API) characterization" and said it "lacks sufficient information to know whether the drug would cause harm when administered to humans".

That is an honest regulatory statement and a UK lab ordering buy bpc-157 vials should read the batch report with it in mind: 99% is a measurement of the chromatogram, not a safety assessment.

Net peptide content: why 10mg is rarely 10mg of peptide

A lyophilised peptide is not pure peptide by weight. It carries water bound to the powder and counter-ions left from purification, most often trifluoroacetate from the HPLC mobile phase, or acetate if the supplier has exchanged it.

Sigma-Aldrich's technical guidance states the point plainly: "Unless requested, all peptides are supplied based upon gross weight." Net peptide content "is typically determined by quantitative amino acid analysis" and "should not be confused with peptide purity" (Sigma-Aldrich, Peptide Quick Tips).

The same note gives the arithmetic. Gross weight multiplied by HPLC purity gives an estimate of full-length peptide, so a 5.1mg vial at 95% purity holds roughly 4.8mg of full-length product before any correction for water and counter-ions. Net peptide content, measured by amino acid analysis, is usually lower again.

Few research-grade certificates report net content, because amino acid analysis is a separate, slower assay. Where it is absent, the sensible reading of "10mg" is "10mg gross".

For a copper complex such as copper peptide ghk-cu the same logic applies with an extra term: the copper ion is part of the mass, and the blue powder is a visual check that the complex is present, not a substitute for the report.

What independent testing of online peptides has found

In 2024 Ashraf and colleagues bought semaglutide from six online vendors operating without prescriptions. Three took the money and sent nothing, demanding further "customs" payments. Of the three products that arrived, LC-MS found semaglutide in all of them but at purities of 7% to 14% "vs advertised 99%", with measured content exceeding the label by 29% to 39%, and one sample showed raised endotoxin at 8.95 EU/mg (Ashraf et al., JAMA Network Open, 2024).

The problem is older than the weight-loss boom; in 2008 Currier and colleagues, working on US military HIV vaccine research, traced false-positive T-cell results to HIV peptides that had arrived from two custom suppliers contaminated with a cytomegalovirus peptide at "approximately 1% by weight", enough to distort a clinical trial assay (Currier et al., Clinical and Vaccine Immunology, 2008). One per cent is within what a lazy reading of "99% pure" would wave through.

A 2026 review in Cureus put the general point well: "Certificates of analysis, purity claims, and biomedical language may provide reassurance, even when products have not undergone the regulatory review, manufacturing oversight, or postmarketing surveillance expected for approved medicines" (Cureus, 2026). A certificate is necessary; it is not sufficient, and a recycled one is worse than none.

The legal context for all of this, including what the MHRA does when a seller's conduct does not match the research label, is covered in a companion post on how research peptides are regulated and sold in the UK.

A checklist for reading a UK supplier's report

Working through a report takes two minutes once the questions are fixed.

• Batch number: does it match the vial label exactly, and is there one report per batch rather than one per product?
• Date: was the test run on this batch, or does the date predate the product's appearance on the site by years?
• Method: is the HPLC method named, with column and detection wavelength, and is the chromatogram shown?
• Identity: is there a mass spectrum with expected and found mass, not just the word "confirmed"?
• Blends: is each component identified separately? A vial of glow peptide carries three peptides and should show three identities.
• Non-peptides: a vial of nad+ uk labs order is not a peptide at all, so the report should use a method appropriate to a dinucleotide rather than a borrowed peptide template.
• Lab: is the testing laboratory identified, and could it be contacted?
• Consistency: does the purity on the report match the purity on the product page, to the same decimal?

LynxLab's answer to the checklist is on each product page: every peptide is tested to 99% purity, the batch report sits beside the price, UK stock is dispatched the same day on orders placed by 6pm, UK delivery is free on every order, and support@lynxlab.co.uk will send the raw file to anyone who asks.

For readers who want the background on what a peptide actually is, how it is made and why it arrives as a powder, see the plain guide to research peptides and their chemistry at what are peptides.

Frequently asked questions

What does 99% purity mean on a peptide certificate?

It means 99% of the UV-absorbing material in the sample eluted as the main HPLC peak, with related impurities making up the remaining 1%. It does not confirm identity, state how many milligrams of peptide are in the vial, or say anything about sterility.

What is the difference between purity and net peptide content?

Purity is a percentage of the chromatogram; net peptide content is a percentage of the vial's weight. Lyophilised peptides carry bound water and counter-ions such as trifluoroacetate, so a 99% pure vial can be well under 99% peptide by mass. Sigma-Aldrich notes peptides are supplied by gross weight unless requested otherwise.

How do I know if a peptide certificate of analysis is fake?

Look for a batch number that matches the vial, a test date that makes sense, a named method, and the actual chromatogram and mass spectrum rather than summary numbers. A single report reused across batches, or a purity figure with no trace behind it, is the common pattern in recycled certificates.

Does HPLC confirm what the peptide is?

No. HPLC measures how clean a sample is, not what it is; a pure sample of the wrong sequence gives a perfect chromatogram. Identity comes from mass spectrometry, which compares the measured mass to the theoretical mass of the stated sequence.

Why do UK peptide suppliers publish lab reports?

Because research peptides are not medicines and have not been assessed by the MHRA, so the batch report is the only quality evidence a buyer has. Published test-purchase studies have found online products at 7% to 14% purity against a claimed 99%, which is the gap a real report is meant to close.

Sources

• HPLC Analysis and Purification of Peptides, Mant et al., Methods in Molecular Biology, 2007
• Liquid Chromatography-High Resolution Mass Spectrometry for Peptide Drug Quality Control, Zhang et al., AAPS Journal, 2015
• Therapeutic peptides: current applications and future directions, Wang et al., Signal Transduction and Targeted Therapy, 2022
• Peptide Quick Tips, Sigma-Aldrich technical documents, Merck
• Safety and Risk Assessment of No-Prescription Online Semaglutide Purchases, Ashraf et al., JAMA Network Open, 2024
• Peptide Impurities in Commercial Synthetic Peptides and Their Implications for Vaccine Trial Assessment, Currier et al., Clinical and Vaccine Immunology, 2008
• Unregulated Peptide Use in the Age of Biohacking, Cureus, 2026