A Certificate of Analysis (COA) is the single most important document a peptide supplier ever hands you. It is the only objective record of what is actually in the vial. Researchers who can read a COA fluently can spot a counterfeit, a degraded batch, or a misbranded product in under 30 seconds. Those who cannot are trusting marketing copy. This guide walks through every field on a peptide COA, what it means, what good numbers look like, and the five fastest red flags that should make you walk away.
What a COA actually is
A Certificate of Analysis is a batch-specific lab report issued by the manufacturer (or an independent third party) certifying the identity, purity, and characteristics of a specific lot of material. For research peptides, a COA should be tied to a unique Lot Number and a manufacture date — not a generic product brochure. If the document does not name a specific lot, it is not a COA. It is a brochure.
Every legitimate research peptide COA contains the following blocks, in some order:
- Product identification (name, CAS number, sequence, molecular formula, molecular weight)
- Lot identification (lot number, manufacture date, expiration or retest date)
- Appearance and physical state
- Identity confirmation (typically mass spectrometry)
- Purity by HPLC
- Water content (Karl Fischer or loss on drying)
- Acetate or TFA counter-ion content (if applicable)
- Endotoxin / bacterial endotoxin test (BET) — for sterile material
- Bioburden / sterility (for sterile material)
- Storage and handling instructions
- Signature, date, and lab credentials
Field by field: what to look for
1. Product identification
The product name should match the sequence and the molecular formula. A common red flag: a COA labeled "BPC-157" with a molecular weight that does not match the published value of 1419.53 g/mol (give or take 0.5 g/mol for salt forms). Cross-check the molecular weight against the published literature. PubChem and the manufacturer's own spec sheet are the easiest references.
The sequence is given in single-letter amino acid code. For BPC-157 this is GEPPPGKPADDAGLV (15 residues). For Semaglutide it is a 31-residue chain with a non-standard modification. For GHK-Cu it is the tripeptide GHK complexed with copper(II). If the sequence is missing, you cannot verify identity. Walk away.
2. Lot number and dates
The lot number should be unique, alphanumeric, and traceable to a manufacture date. Most reputable manufacturers print the lot in the format YYYYMMDD-XXX or similar. Look for both a manufacture date and either an expiration date or a retest date. Lyophilized peptides are typically stable for 24-36 months at -20 °C; reconstituted peptides for 14-28 days at 2-8 °C depending on the molecule.
3. Appearance
"White to off-white lyophilized powder" or "white fluffy lyophilized cake" is the standard. Any mention of yellowing, browning, granular crystals, or oily residue is a hard fail. Color shifts are the earliest visual sign of oxidative degradation.
4. Identity by mass spectrometry
The COA should report the observed mass from either ESI-MS (electrospray ionization mass spectrometry) or MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight). The observed mass should match the calculated monoisotopic mass within 1 Da for peptides under 5 kDa. For larger molecules a deviation of 2-5 Da can be normal due to averaging and isotopic envelopes. If MS data is missing, identity is unverified.
5. Purity by HPLC
This is the most-quoted number on any COA. It is the percentage of the integrated chromatogram area attributable to the target peptide peak, measured by reverse-phase high-performance liquid chromatography (RP-HPLC) at a stated wavelength (usually 214 nm or 220 nm for the peptide bond, occasionally 280 nm for aromatic residues).
Benchmarks for research-grade material:
- ≥ 99% — exceptional, typical of GMP-adjacent production
- ≥ 98% — strong, the de facto standard for serious research suppliers
- ≥ 95% — acceptable for many research applications; below this, impurity profiles matter more than the headline number
- < 95% — questionable for any quantitative work
Look at two things, not one: the headline purity number and the chromatogram itself if it is attached. A clean trace shows a single dominant peak with a flat baseline and minimal shouldering. Multiple peaks of similar height, broad humps, or unidentified peaks above 1% are warning signs even if the headline number looks fine.
6. Water content
Lyophilized peptides retain residual moisture. Karl Fischer titration is the gold standard. Acceptable values are typically < 8% by mass, ideally < 5%. High water content reduces the actual peptide mass per vial (a 5 mg vial at 10% water content gives you only 4.5 mg of dry peptide) and accelerates hydrolytic degradation.
7. Counter-ion content (acetate or TFA)
Most synthetic peptides are isolated as acetate or trifluoroacetate (TFA) salts. Acetate is preferred for research use; TFA can interfere with some assays at high concentrations. The counter-ion mass is part of the total vial mass — a 5 mg "peptide content" vial may weigh 5.5-6 mg total once counter-ion and water are accounted for. Reputable suppliers report net peptide content separately from gross mass.
8. Endotoxin (BET) and bioburden
For any peptide intended for reconstitution and sterile handling, the COA should report a bacterial endotoxin test result — typically by LAL (Limulus amebocyte lysate) assay or recombinant Factor C — with a numeric result in EU/mg (endotoxin units per milligram). Research-grade material is commonly < 10 EU/mg; sterile-grade material targets < 1 EU/mg. Bioburden (total aerobic microbial count) should be reported as CFU/g or noted as "not detected" by a validated method.
9. Signature and lab credentials
A COA should be signed (or digitally signed) by a named QC officer, dated, and reference the testing laboratory. Anonymous COAs without an issuing authority are not credible. Independent third-party COAs from ISO 17025-accredited labs are the gold standard; in-house QC from an established manufacturer with a published quality system is acceptable.
Five fastest red flags
- No lot number. If the document does not identify the specific batch it describes, it is marketing material, not a COA.
- No mass spectrometry data. Identity is unverified. The vial could contain anything with the right molecular weight.
- HPLC purity given without a chromatogram or method. A bare "99.5%" with no method, no column, no wavelength, and no trace is unverifiable.
- Endotoxin field missing or marked "N/A" on sterile-intended material. Endotoxin must be measured, not asserted.
- Identical COAs across lots. If two different lot numbers produce byte-identical purity, water content, and chromatograms, the document is fabricated. Real testing produces variation.
How to verify a COA you have been given
- Match the lot to the vial. The lot number on the COA must appear on the physical vial label. If it does not, the COA is not for your material.
- Check molecular weight against PubChem. Open PubChem, search the peptide name, and compare the listed molecular weight (within 0.5 g/mol for the free peptide, +60 g/mol per acetate counter-ion).
- Sanity-check the sequence. Use an online molecular weight calculator (e.g. Bachem's peptide calculator) and confirm the stated MW matches the sequence in single-letter code.
- Ask for the chromatogram. A reputable supplier will share the raw HPLC and MS traces on request. Refusal is a signal.
- Ask which lab ran the tests. "In-house" is acceptable if the manufacturer publishes its quality system. "We can't say" is not.
Quick reference: what a clean COA looks like
- Specific lot number, manufacture date, retest/expiration date
- Product name + sequence + CAS (where assigned) + molecular formula + molecular weight
- Appearance: white to off-white lyophilized powder
- Identity: ESI-MS or MALDI-TOF observed mass matching calculated mass within 1 Da
- Purity: ≥ 98% by RP-HPLC at 214 nm, with method described and chromatogram available on request
- Water content: < 5% by Karl Fischer
- Counter-ion: acetate, content stated, net peptide content reported separately
- Endotoxin: < 10 EU/mg by LAL or recombinant Factor C (sterile-grade: < 1 EU/mg)
- Signature, date, lab credentials
Every Nexphoria peptide ships with a lot-specific COA that includes identity by ESI-MS, purity by RP-HPLC at 214 nm with the chromatogram available on request, Karl Fischer water content, and net peptide content. Lot numbers on the COA match the vial label. We share testing methods and chromatograms on request. Sterile-grade material additionally includes LAL endotoxin results.
All Nexphoria products are sold for in vitro research and laboratory use only. Not for human or veterinary use. Not a drug, food, or cosmetic. This article is educational and applies to peptide products generally; it is not a recommendation for any specific application.