How to read a peptide Certificate of Analysis

A Certificate of Analysis (COA) is the document a peptide manufacturer or third-party laboratory issues to attest that a specific batch of product meets a defined specification. Done well, a COA gives you traceable identity, purity, and quality data for the exact vial in your hand. Done badly — or fabricated — it is a marketing prop that misrepresents what is actually in the bottle.

This guide walks through the structure of a legitimate peptide COA, what each field tells you, what good values look like, and the patterns that distinguish a credible document from a fake.

What every legitimate COA includes

A complete COA is not a one-page certificate of branding. It is a technical document that should let an independent analyst reproduce the result. At minimum, expect:

Vendor or laboratory identity. Company name, full address, contact details, and the name and signature of the certifying analyst.
Batch or lot number. A unique alphanumeric identifier traceable to the specific synthesis run.
Manufacturing and retest dates. When the batch was produced and when its quality should be re-evaluated.
Product identity. Peptide name, sequence in single-letter amino acid code, molecular formula, exact molecular weight, and CAS number where one exists.
Test methods. Each result should reference its analytical method — for example "Purity by HPLC, Method USP <621>" or "Identity by LC-MS, m/z observed vs theoretical."
Specification and result. Each parameter shows the acceptance specification (e.g. ≥98.0% purity) and the actual measured value (e.g. 99.1%).
Conclusions and signatures. A statement that the batch passes specification, signed and dated by the named analyst with enough contact information to allow independent verification.

Documents that do not include these foundational elements are not reliable. The International Council for Harmonisation's Q6B guideline on specifications for biotechnological and biological products formalises what a complete release specification should contain; peptide manufacturers operating to a credible standard align with it.

Reading purity correctly

The purity field is the most-cited number on any peptide COA and the most commonly misread. A peptide COA expresses purity as an HPLC area percent — the proportion of the total UV-absorbing peak area on a high-performance liquid chromatography trace that corresponds to the target peptide.

A few points to internalise:

Area percent is a relative measure. "99% purity" means 99% of what the detector observed at a given wavelength was the target peptide. It does not account for material that does not absorb at the detection wavelength — counterions, residual water, certain residual solvents, or non-chromogenic impurities. Real total content can be lower than the headline number suggests.
The detection wavelength matters. Peptides are typically monitored at 215 nm (peptide bond absorbance) and 280 nm (aromatic residues — tryptophan, tyrosine, phenylalanine). A complete COA reports both, or notes the wavelength chosen and why.
Specifications are usually banded. ≥95% is common for research-grade peptides; ≥98% indicates a tighter specification; ≥99% is achievable for well-purified analogues but is not universal. Claimed purities above 99.9% should be questioned. Mathematically, HPLC integration noise alone often spans 0.1–0.3% area, so "99.99%" without specifying the integration method is not credible.

If a vendor states purity but the COA does not include the underlying HPLC chromatogram, the number is unverifiable. Reputable manufacturers attach the trace as a separate page or PDF.

Identity verification

Purity tells you how much of the product is uniform — it does not tell you what the product actually is. That is the job of mass spectrometry.

Two methods dominate:

LC-MS (liquid chromatography-mass spectrometry) couples HPLC separation to a mass detector. The observed mass-to-charge (m/z) ratio is compared against the theoretical molecular mass of the peptide sequence. For a peptide like BPC-157 (15 residues, theoretical mass approximately 1419.5 Da), the COA should show an observed mass within ±0.5 Da of theoretical, typically as the [M+H]+, [M+2H]2+, and [M+3H]3+ adducts.
MALDI-TOF (matrix-assisted laser desorption/ionisation time-of-flight) is an alternative for larger or more hydrophobic peptides where LC-MS sensitivity is limited. The output is a discrete peak on the m/z axis at the expected mass.

A COA that lists purity without an identity confirmation is incomplete. Purity confirms uniformity; identity confirms that the uniform substance is the one you expected. Both are required to claim authenticity.

For more advanced sequence verification — required for peptides going into clinical research — peptide mapping enzymatically digests the peptide into fragments, separates them, and identifies each fragment by mass. This goes beyond what a routine research COA includes but is standard for therapeutic peptide release.

Quality attributes beyond purity

A peptide COA that stops at purity and identity is incomplete. Several additional parameters are routinely characterised on a credible certificate:

Counterion content. Peptides synthesised by solid-phase methods are typically isolated as salts. The most common counterion is trifluoroacetate (TFA), introduced during deprotection and cleavage. TFA-salt peptides can contain 5–25% TFA by mass — meaning a vial labelled "5 mg peptide" may contain only 4 mg of the actual peptide and 1 mg of TFA. Some manufacturers convert to acetate salts for better solubility and lower toxicity at high doses. The COA should specify the counterion and quantify it.
Water content (Karl Fischer). Lyophilised peptides absorb atmospheric moisture. Water content is measured by Karl Fischer titration. Typical values for freshly lyophilised peptides are 2–8% by mass. Higher values indicate poor lyophilisation or product that was reconstituted and re-dried.
Residual solvents. Peptide synthesis uses solvents like DMF, DCM, NMP, and acetonitrile. Residues are quantified by gas chromatography against the ICH Q3C limits. Class 1 solvents (benzene, carbon tetrachloride) should be undetectable; Class 2 limits apply for the typical synthesis solvents.
Bacterial endotoxin. For peptides intended for injection or cell-culture work, endotoxin (lipopolysaccharide from gram-negative bacterial cell walls) is tested by Limulus Amebocyte Lysate (LAL) assay per the United States Pharmacopeia's General Chapter <85>. A typical specification is below 1 EU/mg, though research-only material is often not tested for endotoxin at all — a gap worth knowing about.
Microbial limits. Aerobic bacterial count, yeast, mould, and pathogen specifics per USP <61>/<62>.

A COA from a third-party laboratory that includes counterion content, water content, residual solvents, and endotoxin alongside identity and purity is performing the full characterisation a reproducible experiment requires. Most research-peptide COAs include only identity and purity and skip the rest — not necessarily a red flag, but information you should not assume is present.

Red flags

The following patterns appear on fabricated or misleading COAs.

Claimed purity above 99.9% without a chromatogram or stated integration method.
No batch or lot number, or batch numbers that follow a sequential predictable pattern across products (suggesting fabrication rather than real synthesis runs).
Missing test methods. A line that reads "Purity: 99%" with no method reference is not a measurement, it is an assertion.
No analyst signature or contact information. A COA without a named, contactable analyst cannot be independently verified.
Dates that do not reconcile. The COA issue date is before the manufacturing date, or the retest date is unreasonably far in the future (ten or more years for a peptide is implausible).
Generic template language. The same boilerplate sentences and certificate text appearing verbatim across products from different listed manufacturers — a classic indicator of a copied template.
Inconsistent typography or alignment. Mixed fonts, misaligned columns, and low-resolution logos suggest edited documents.
Pass/fail only. Results given as "PASS" without numerical values are not analytical data; they are claims.
No laboratory address or accreditation. A credible third-party laboratory carries a postal address and, ideally, ISO/IEC 17025 accreditation — the international standard for the competence of testing and calibration laboratories.

Any single red flag is reason to ask the vendor for clarification. Three or more together is reason to discard the COA entirely.

Third-party versus in-house COAs

A COA produced by the same company that synthesised the peptide — an in-house COA — is a starting point. The manufacturer is attesting to its own work, which means there is no independent check.

A third-party COA is produced by a laboratory with no commercial interest in the product. The sample is sent in, analysed against agreed methods, and the result is reported back regardless of outcome. Several laboratories specialise in this for research peptides, including Janoshik Analytical, Echelon Biosciences, and a small set of contract labs. Third-party COAs reduce the conflict-of-interest problem inherent in self-certification.

Two structural advantages of independent testing:

Method neutrality. The third-party laboratory has no incentive to pick analytical parameters that flatter the result. An in-house lab might integrate HPLC peaks generously to boost reported purity; a third-party lab gives you the trace and the integration software's default values.
Accreditation. A laboratory accredited to ISO/IEC 17025 has demonstrated to an external accreditation body that its measurements are technically valid and traceable. Accreditation is voluntary and expensive, which is precisely why a laboratory that has earned and maintained it signals a real commitment to measurement quality.

For research peptides where the user's safety depends on what is actually in the vial, third-party COAs are not a luxury — they are the only practical mechanism to verify identity and purity without doing the analytical work yourself.