Quality & Purity
At Peptide.Express, purity is not a selling point. It is the baseline requirement. Every peptide we supply undergoes strict multi-stage testing before it reaches your lab.
HPLC Verification
Every batch is analyzed by reverse-phase High-Performance Liquid Chromatography (HPLC) to establish purity as area under the curve. The threshold across the entire catalog is ≥99%. Certificates of Analysis are published for every product listing.
Mass Spectrometry (LC-MS/MS)
Liquid Chromatography-Tandem Mass Spectrometry measures the molecular weight of the eluting compound and checks it against the published value. Purity tells you how much. Mass tells you what.
Supply Chain Integrity
Every batch carries chain-of-custody documentation from raw material sourcing through final lyophilization and packaging, so any result traces back to the exact lot it came from.
Endotoxin & Sterility Testing
Batches undergo LAL (Limulus Amebocyte Lysate) endotoxin testing and microbial contamination screening, with the endotoxin figure reported per batch. Endotoxin is heat-stable and survives sterile filtration, which is why it is measured separately rather than inferred from sterility.
Third-Party Independent Testing
Peptide.Express does not run its own purity testing. Independent accredited laboratories produce every figure we publish, which removes the incentive a lab has to pass its own material and creates an external chain of custody.
Certificates of Analysis (CoA)
A batch-specific Certificate of Analysis accompanies every product. Each CoA carries the HPLC chromatogram and purity result, LC-MS/MS mass data, appearance, solubility notes, endotoxin result, test date, and the name of the testing laboratory.
≥99%
Minimum Purity
100%
Third-Party Tested
100%
Batch-Level CoA
Testing Methodology
Five checks run on every batch before it is listed. Each answers a different question, and none of them substitutes for another.
| Test | Method | What It Confirms | Pass Threshold |
|---|---|---|---|
| Purity | HPLC (reverse-phase C18) | Proportion of target peptide vs impurities, by area under the curve | ≥99% |
| Identity | LC-MS/MS | Molecular weight matches the published value for the compound | Exact mass match |
| Endotoxin | LAL (Limulus Amebocyte Lysate) | Gram-negative bacterial endotoxin content | Reported per batch |
| Appearance | Visual QC | Physical form, colour, particulate matter | White to off-white powder (GHK-Cu and GHK-Cu blends are deep blue) |
| Solubility | Reconstitution test | Complete dissolution in standard diluents | Full dissolution, no visible cake |
What HPLC Tells You — And What It Doesn't
Reverse-phase HPLC separates a peptide sample by hydrophobicity. The sample is driven through a C18 column under pressure with a water/acetonitrile gradient, and a detector records absorbance as each species elutes. The output is a chromatogram: peaks against a time axis. Purity is the area of the target peak divided by the total area of every peak on the trace, expressed as a percentage.
That definition carries two limits worth stating plainly.
HPLC does not identify the impurities. A batch reported at ≥99% has a remaining fraction of under 1%, and the chromatogram says nothing about what is in it. Truncated sequences from incomplete coupling steps, deletion sequences missing a residue, residual trifluoroacetate from purification, solvent traces — these all appear as small peaks with retention times, not as identified compounds. Characterising them takes a separate analysis.
HPLC does not confirm the main peak is the right molecule. A chromatogram showing a single sharp peak at 99.4% is evidence of a clean, homogeneous sample. It is not evidence that the sample is the peptide named on the label. Retention time is characteristic but not diagnostic — two peptides of similar hydrophobicity can co-elute or elute within seconds of each other. Purity by HPLC is a statement about homogeneity. Nothing more.
Vendors who publish an HPLC percentage and stop there are reporting one dimension of two and letting the reader assume the second. We would rather say where the method ends. Peptide characterisation practice, and the reason mass spectrometry is run alongside chromatography rather than instead of it, is documented across the analytical literature: FDA guidance: Analytical Procedures and Methods Validation for Drugs and Biologics.
What LC-MS/MS Adds
Liquid chromatography coupled to tandem mass spectrometry closes the gap HPLC leaves open. The chromatography stage separates the sample; the mass spectrometer then measures the mass-to-charge ratio of what elutes and compares it against the theoretical molecular weight for the named compound. Purity says how much. Mass says what.
TB-500 is the clearest illustration of why this matters. The name is applied across the research market to at least two different molecules. One is full-length synthetic Thymosin β-4, a 43-residue peptide with a molecular weight of 4,963.4 Da. The other is a short fragment built around the LKKTET actin-binding motif, weighing in around 890 Da depending on the exact fragment and any N-terminal acetylation. Both ship under the label "TB-500". They are not the same compound, they do not behave the same way in an assay, and a researcher who assumes one and receives the other has a protocol built on the wrong molecule.
No purity figure distinguishes them. Both can be 99% pure. The mass on the Certificate of Analysis is the only reliable way to know which one is in the vial — roughly 4,963 Da or roughly 890 Da, and the difference is not subtle. Read the mass field before you read the purity field.
Why Independent Third-Party Testing
A laboratory that tests material it produced has an interest in the outcome. That is not an accusation of misconduct — it is a structural problem with self-verification that exists regardless of anyone's intentions. When the party running the assay is the party that loses money if the assay fails, the result is not an independent check.
Sending each batch to an outside facility removes the incentive entirely. The laboratory that runs the HPLC and the mass spec has no stake in whether a lot passes. It also produces something a self-issued document cannot: a verifiable external chain of custody. The CoA names the facility, the batch, and the date, and that record sits outside our organisation.
Peptide.Express does not conduct in-house testing. Every purity and identity figure published on this site originates from an independent laboratory. Supplier certificates that arrive with incoming material are treated as a starting point, not a result — a lot is unverified until our own third-party analysis clears it. Batch certificates are published in the lab results library.
How to Read Your Certificate of Analysis
A CoA is a batch record, not a brochure. Each field answers something specific, and the fields are not interchangeable in importance — start with the lot number and work down.
Compound name
The full chemical or accepted scientific name, not the marketing name. If your vial says "Wolverine Blend" and the CoA says "BPC-157" and "TB-500" as separate line items, that is correct — the document reports on the molecules, not the SKU.
Batch / lot number
The single most important field. It ties this document to one specific synthesis run. The number printed on your vial label should appear here verbatim.
HPLC purity result and chromatogram
A percentage plus the trace it was calculated from. The chromatogram matters as much as the number: you are looking for one dominant peak with a clean baseline, not a headline figure sitting on its own.
LC-MS/MS mass data
The observed molecular weight against the theoretical value for the named compound. Agreement here is what turns a purity figure into a purity figure for the right molecule.
Appearance
Physical form and colour as observed at QC. White to off-white lyophilized cake for most compounds. GHK-Cu is the exception — the copper complex is deep blue, as are blends containing it such as KLOW, and a pale or colourless GHK-Cu solution is the abnormal result.
Endotoxin result
The LAL assay figure for that batch, reported in endotoxin units. Relevant to cell-culture work, where endotoxin at low concentrations shifts cytokine readouts and quietly corrupts an assay.
Test date
When the analysis was run. A CoA dated well before the synthesis date on the vial is a document that belongs to a different lot.
Testing laboratory
The named facility that performed the analysis. On our CoAs this is an independent third-party laboratory, not Peptide.Express.
One CoA, one batch. Certificates are not shared across a product line. Reorder the same compound three months later and it will very likely come from a different synthesis run with its own document and its own numbers. The lot number on the vial maps to exactly one record — that mapping is the whole point of the system. Reconstitution handling for the compound you received is covered in the peptide reconstitution protocol guide, and the hazard classification, personal protective equipment, storage incompatibilities and disposal route for it are in that compound’s Safety Data Sheet.
Quality & Purity Testing FAQ
What does ≥99% purity mean for a research peptide?
It means that at least 99% of the peptide material in the vial, measured as area under the curve on an HPLC chromatogram, corresponds to the target peptide. The remaining fraction is typically truncated sequences, deletion sequences, residual synthesis reagents, or counter-ions such as trifluoroacetate. Purity is a proportion, not a guarantee of what the other 1% is. It is also a mass-independent figure — a 99% pure 5 mg vial and a 99% pure 10 mg vial carry different absolute impurity loads.
What is HPLC and how is it used to test peptides?
High-Performance Liquid Chromatography separates the components of a sample by pushing it through a packed column under pressure. For peptides the standard is reverse-phase C18: the column is nonpolar, the mobile phase is a water/acetonitrile gradient, and molecules elute in order of hydrophobicity. A detector records absorbance as material leaves the column, producing the chromatogram. Purity is calculated by integrating the area of the target peak against the total area of all peaks.
What does LC-MS/MS confirm that HPLC cannot?
Molecular identity. HPLC tells you that one species dominates the sample; it does not tell you which species that is. LC-MS/MS measures the mass-to-charge ratio of the eluting molecule and compares it against the theoretical molecular weight of the named compound. A peak at 99% purity means nothing until the mass confirms that peak is the peptide on the label.
What is LAL endotoxin testing?
LAL stands for Limulus Amebocyte Lysate — a reagent derived from horseshoe crab blood that clots in the presence of bacterial endotoxin, the lipopolysaccharide fraction of Gram-negative bacterial cell walls. Endotoxin is heat-stable and survives sterile filtration, so a sterile preparation is not automatically a low-endotoxin preparation. The distinction matters most in cell-culture research, where endotoxin activates TLR4 signalling and produces inflammatory readouts that have nothing to do with the compound under study. Endotoxin results are reported per batch on the CoA.
Why does Peptide.Express use independent third-party testing?
Because a laboratory testing its own material has an interest in the result, and an interested party is not a check. Sending each batch to an outside facility removes that incentive and creates an external chain of custody — a document produced by an organisation with no stake in whether the batch passes. Peptide.Express does not conduct in-house purity testing. The purity and identity figures published on this site come from the independent laboratory named on each CoA.
How do I read a Certificate of Analysis?
Start with the lot number and check it against the vial in front of you — everything else on the page is only meaningful if those match. Then read the HPLC section: the purity percentage and the chromatogram it was derived from. Then the LC-MS/MS mass data, confirming identity. Then appearance, endotoxin, test date, and the name of the testing laboratory. CoAs are batch-specific documents, not product-line documents: two vials of the same compound from different synthesis runs have two different CoAs.
What is the difference between peptide purity and peptide identity?
Purity is a proportion. Identity is a fact about the molecule. A sample can be 99.5% pure and still be the wrong compound — the chromatogram would look immaculate. This is why purity and identity are tested by two different instruments and reported as two separate results.
What should I do if the batch number on my vial does not match the CoA?
Treat the CoA as not applying to that vial and contact support@peptide.express with the lot number printed on the label. A mismatch usually means the wrong document was attached rather than a problem with the material, but the fix is to retrieve the correct batch record — not to assume the numbers are close enough. Do not use the material in an experiment whose results depend on documented purity until the correct CoA has been supplied.
Research Use Disclaimer
All products listed on Peptide.Express are supplied for in-vitro laboratory research and educational purposes only. Nothing on this page is medical advice, and no compound described here is intended for human consumption, clinical use, or veterinary use.