How to Read a Peptide COA — a Buyer's Guide
Every EU peptide vendor publishes a Certificate of Analysis (COA). Most look authoritative; many are misleading. This guide walks through what each field on a COA actually means, why some labs matter more than others, and how to spot a COA that's been copy-pasted from a template.
The seven parameters
A fully comprehensive peptide COA covers seven parameters. Most EU vendors stop at two or three. Where a vendor is sitting on that spectrum is the most important testing signal on their review.
High-Performance Liquid Chromatography — measures what percentage of the sample is the target peptide versus related impurities. Industry standard for research peptides: ≥ 98%; premium EU vendors claim 99%+. This is the minimum every COA must include.
Liquid Chromatography – Mass Spectrometry confirms that the molecular mass of the peak matches the expected peptide. HPLC alone could miss a different peptide at similar retention time; LC-MS anchors identity. A professional COA includes the observed m/z and expected m/z side by side.
Fourier-Transform Infrared Spectroscopy confirms that the peptide's secondary structure matches reference. Catches post-synthesis folding or aggregation that HPLC and LC-MS can miss. Research Peptides Europe is the only EU vendor that publishes FTIR as standard.
Chemiluminescent Nitrogen Detector measures actual peptide content— grams of peptide per gram of sample. HPLC purity is relative (is the target 99% of what passes through the column?); CLND is absolute (how much peptide is actually in the vial?). A vial can be 99% pure by HPLC and only 70% peptide by CLND — the remainder is water, salts, and counter-ions from synthesis. Particle Peptides is the only EU vendor reporting CLND as a standard parameter. If you're buying by weight and care what you're actually dosing with, CLND is the parameter that matters.
Limulus Amebocyte Lysate assay — measures bacterial endotoxin contamination. Report format: EU/mg with a specified limit per European Pharmacopoeia. A meaningful entry looks like "0.12 EU/mg, limit 10 EU/mg." A vague "LAL: pass" without numbers is softer.
ICH Q3D elemental impurity analysis. Class 1 (As, Cd, Pb, Hg) and Class 2 (Co, V, Ni) residues from synthesis catalysts. Ph. Eur. has per-element daily-exposure limits; a proper COA reports each element in parts-per-million versus limit.
Total Aerobic Microbial Count and Total Yeast & Mold Count. Detects microbial contamination during synthesis or handling. Reported in colony-forming units per gram (CFU/g) against Ph. Eur. thresholds.
The lab matters as much as the methods
Two COAs claiming "99% HPLC purity" are not equivalent if one is an in-house result and the other is an independent Janoshik Analytical (Czech Republic) result. Independent labs have no incentive to round up; in-house labs work for the vendor.
The community-standard independent lab for research peptides is Janoshik Analytical. Vendors who publish Janoshik reports — QSC Peptides, PeptidesDirect, Research Peptides Europe — carry stronger testing-transparency signals than vendors who publish only in-house COAs. Particle Peptides publishes independent multi-lab blind testing, an even higher bar.
Signs of a template COA
- No batch / lot number, or a batch number that doesn't appear on the vial you received
- No date, or a date more than 12 months old for a "current" batch
- No lab name, or a lab name with no online presence
- No peptide sequence specified
- Identical-looking COAs across multiple peptides (same layout, same numbers, different headers)
- Purity reported as a round "> 99%" with no decimal, no actual chromatogram image, no method parameters (flow rate, column, gradient)
See our vendor rejection framework for how COA quality plays into our overall vendor scoring.
COA depth across EU vendors
| Vendor | Parameters | Lab |
|---|---|---|
| Particle Peptides | 7 (HPLC, LC-MS, FTIR, CLND, LAL, heavy metals, bioburden) | Independent blind multi-lab |
| Research Peptides Europe | 6 (HPLC, LC-MS, FTIR, LAL, heavy metals, bioburden) | In-house + third-party |
| QSC Peptides | 3+ (HPLC, LC-MS, Janoshik verification) | Janoshik Analytical (independent) |
| PeptidesDirect | 2–3 (HPLC, LC-MS; Janoshik batch-testing) | Janoshik Analytical |
| PeptideProduct EU | 1 (in-house COA per batch, limited detail publicly) | In-house |
FAQ
What is the minimum a legitimate COA must contain?
Batch / lot number, date of testing, lab name, peptide name and stated sequence, test method (HPLC is the minimum), purity percentage, and signature or stamp. Anything less is a marketing document, not a COA.
What is the difference between purity and peptide content?
Purity (HPLC) measures what percentage of the peptide in the vial is the target peptide versus related impurities. Peptide content (typically CLND detector) measures how much actual peptide is in the vial — the rest is mostly residual water, salts, and counter-ions from synthesis. A vial can be 99% pure by HPLC but only 70% actual peptide by CLND. Particle Peptides is currently the only EU vendor that reports CLND peptide content as a standard parameter.
How much does FTIR add beyond HPLC and LC-MS?
FTIR (Fourier-Transform Infrared Spectroscopy) confirms structural integrity — that the peptide hasn't folded, aggregated, or degraded post-synthesis. HPLC confirms how pure it is, LC-MS confirms the correct molecular mass is present, FTIR confirms the molecule is structurally intact. Research Peptides Europe is the only EU vendor using FTIR as standard. It catches a small class of defects the other two methods miss.
What should I look for in an endotoxin test?
The Limulus Amebocyte Lysate (LAL) assay is the industry standard. Result should be reported in EU/mg with a specified limit. Ph. Eur. limits vary by intended route — parenteral research has tighter thresholds than topical. An "LAL: pass" with no number is softer than "LAL: 0.12 EU/mg, limit 10 EU/mg."
Does a single comprehensive COA cover the whole batch?
It should. One COA should cover one lot number. When you receive a vial, the lot number on the label should match a published COA — ideally accessible on the vendor site without placing an order (Particle's COA Vault is the cleanest example). If the lot on your vial is not in the public database, the COA you're shown isn't for your product.
What about bioburden and heavy metals?
Bioburden (TAMC: Total Aerobic Microbial Count, TYMC: Total Yeast and Mold Count) checks for microbial contamination during synthesis or handling. Heavy metals screening checks for class 1 (arsenic, cadmium, lead, mercury) and class 2 (cobalt, vanadium, nickel) residues from synthesis catalysts. Both are Ph. Eur. parameters; a full 7-parameter COA includes them. Many "comprehensive" COAs stop at HPLC + LC-MS + endotoxin and omit these — worth noting.