How to Read a Certificate of Analysis

A Certificate of Analysis is the document that turns a vendor's purity claim into something verifiable. It records what tests were performed on a specific batch, by what laboratory, on what date, and with what result. This article walks through every field on a typical research peptide COA, what each one means, and what should make a researcher reject the batch entirely.

The verification stakes are real: an ISO/IEC 17025-accredited laboratory operates under externally audited methods, while a vendor-issued "house COA" answers to no one. The distinction is what this article makes operational. It pairs with the deeper material in our testing methodology overview and the introductory framing in Testing & COAs.

What is a Certificate of Analysis?

A Certificate of Analysis is a document issued by an analytical laboratory that records the test results performed on a specific batch of material. It is not a marketing claim, a product brochure, or a generic purity statement. It is a record of physical events: this material was tested on this date, by this analyst, at this laboratory, using these methods, and these were the readings.

The distinction between a real COA and a marketing-graphic-styled-as-a-COA is the central question this article answers. Marketing graphics are common in the research peptide category — by some industry estimates, more than half of public-facing "COAs" in this space lack a verifiable issuing laboratory. A real document carries certain artifacts that a graphic mocked up in design software does not: a laboratory letterhead, a defined methodology section, instrument identifiers, an analyst signature. Knowing what those artifacts look like is the verification skill.

Which fields should appear on every COA?

A complete COA for a research peptide contains seven required fields. Missing any one of them is grounds to ask the vendor for a corrected document before treating the certificate as valid. The table below summarizes each field, what it should contain, and the red flag that signals a fabricated or recycled document.

Issuing laboratory

The laboratory header is the document's first authority signal. Look for the lab name, physical address, phone number, and contact email — the address should be a real building, not a mail-drop service. The most reliable accreditation reference is ISO/IEC 17025:2017, the international standard for the competence of testing laboratories. Holders are externally audited on methods, equipment calibration, and personnel qualifications, and accreditation numbers can be looked up against the registrar's public database.

Document identifier and date

A COA carries its own document identifier — a unique number the issuing lab assigns when the report is generated. Pair the identifier with the date of issue: a recent COA carries a recent date. Most lyophilized research peptides have characterized stability windows in the 12–24 month range; a certificate dated more than two years before the shipment date is referencing material that is almost certainly long since exhausted, and the document is being reused as a generic stand-in.

Material identification

The compound being tested has to be named precisely. For a peptide, that means an IUPAC or common name (e.g., Cagrilintide, BPC-157), the molecular formula, the theoretical molecular weight, and a CAS registry number where one is assigned. The vendor catalog name can appear too, but the molecular details are what matter — they are what the testing actually verifies.

Batch (lot) number

The batch number is the load-bearing field. The number printed on the vial in your hand should match the batch number on the COA exactly. If it doesn't match, the COA refers to a different batch — possibly a previously-tested batch the vendor recycles as a generic certificate. The deeper distinction between batch-matched and generic documents is its own topic, covered in batch-matched vs. generic COAs.

Test methodology

Every test on the certificate names the method used. For purity, expect HPLC or RP-HPLC with the column type, mobile phase, gradient parameters, and detection wavelength. For identity, expect ESI-MS (electrospray ionization mass spectrometry) with the observed mass-to-charge ratio. For endotoxin, expect LAL (Limulus Amebocyte Lysate) or rFC (recombinant Factor C) with the assay variant. Methodology references that point to a published standard — USP <85> for endotoxin, USP <621> for HPLC system suitability — are a strong signal of a real testing operation. The deeper method-by-method walkthrough lives in our cornerstone on the three core analytical methods.

Identity confirmation

The identity section confirms the material in the vial matches what the label claims. Mass spectrometry is the standard method, and the COA should report the theoretical molecular weight (calculated from the peptide's amino acid sequence) alongside the observed value (measured by the instrument). If they match within the instrument's tolerance — typically a few daltons for low-resolution systems, sub-dalton for time-of-flight or Orbitrap instruments — identity is confirmed. A printed mass spectrum, rather than a numeric pass/fail, is the strongest evidence the test was actually performed.

Purity by HPLC

High-Performance Liquid Chromatography separates the target peptide from impurities and quantifies the relative proportion of each. The result is a percentage — 99.2%, 99.8%, etc. — calculated by integrating the area under the target peak divided by the total area of all peaks in the chromatogram. The chromatogram itself, not just the percentage, is what makes the result verifiable. A reasonable chromatographic resolution limit sits around 0.1% area, which is why the working ≥99% purity threshold is method-anchored rather than arbitrary, and why reading the chromatogram visually is part of evaluating a real report.

Endotoxin result

Bacterial endotoxin contamination — lipopolysaccharide from Gram-negative bacterial cell walls — can compromise research applications even at low concentrations. A complete COA reports endotoxin either as a numeric value in endotoxin units per milligram (EU/mg) or as a pass/fail against a defined threshold. Numeric values carry more information; a pass/fail tells you the material met some threshold, but the threshold itself can vary by intended research use.

Appearance, water content, and ancillary tests

A complete COA records ancillary observations that purity testing alone might miss: visual appearance of the lyophilized cake (typically "white to off-white powder"), water content by Karl Fischer titration (residual moisture from the lyophilization process), and pH of a reconstituted solution. Anomalies — discolored material, residual moisture above ~2%, unexpected pH — are flags worth raising with the vendor before you accept the batch.

Analyst signature and date of analysis

The COA closes with the name (or initials) of the analyst who performed the testing, the date the analysis was completed, and ideally a signature or stamp. The analyst is the person whose competence is being attested. Without a name or initials, there is no accountability, and the certificate becomes anonymous — which materially weakens its evidentiary value. As the ISO/IEC 17025:2017 guidance puts it, the report should "include all the information requested by the customer and necessary for the interpretation of the test results."

How do you verify a COA before accepting a batch?

Reading the document is the first step; verifying it is the second. Even a complete-looking COA can be fabricated, and the verification protocol is straightforward — five checks against the physical material, the dates, the methodology, the laboratory, and the vendor's records. Run all five before you treat the document as evidence; any failure is a stop-and-ask event.

1. Match the batch. Confirm the batch number on the COA matches the batch number on the physical vial label. If they don't match, stop here — the document does not refer to your material.
2. Match the date. The date of analysis should be reasonable for the material in your hand: within months, not years.
3. Match the methodology references. If the COA cites USP <85> for endotoxin, that's verifiable against the published standard. If it cites a method that doesn't exist or doesn't apply, that's a red flag.
4. Look up the laboratory. A real lab has a website, a phone number that reaches a person, and ideally an accreditation registration. Call the number and confirm the document identifier on file.
5. Cross-check with the vendor. A reputable vendor can produce the same COA on request. Email the order reference and product, and confirm the document they send back matches the document you already have.

The deeper request-and-verify workflow — including how to phrase the request and what to do when the vendor stalls — is its own topic, covered in requesting and verifying a COA before purchase.

Which red flags should make you reject a batch?

Some patterns are common enough in this category that any single one is grounds to refuse the material and ask for a different batch — or a different vendor. Each flag below has been seen on documents circulated as legitimate COAs in the research peptide market.

• No batch number. A COA without a batch number is not a COA. It is a generic statement.
• Batch number mismatch. The number on the COA does not match the number on the vial.
• No issuing laboratory. No letterhead, no contact information, no way to reach the lab that supposedly performed the testing.
• No analyst attribution. No name, no initials, no signature.
• No methodology references. "Tested for purity" with no specification of how.
• Stale date. A date of analysis that predates the vendor's claimed batch synthesis date, or that is older than what the material's shelf life would allow.
• Identical COA across multiple batches. If two physical vials with different batch numbers come with what is clearly the same scanned document, the document is being reused — and at most one of those batches was actually tested.
• Stated values too clean. A COA that reports purity to four decimal places without a chromatogram, or endotoxin as exactly "<0.0 EU/mg," is more likely fabricated than a document that reports "99.4%, see attached chromatogram, peak area 99.41%, area-norm method" — the latter is the texture of real instrument output.

How does Nexara batch-match every shipment?

Every shipped batch is independently tested before it leaves the facility, and the batch number printed on each vial corresponds to a specific COA record on file. When a customer requests a COA, the request is matched against the batch number from their order, and the matching document is retrieved and emailed back — typically within one business day. The same operating posture is documented across our quality standards and the cold-chain practice that protects integrity in transit.

COAs are currently delivered on request — email nate@nexaralabsusa.com with the order reference and product, and the matching COA is sent within one business day. Direct PDF downloads from product pages are being added as the laboratory partners deliver electronic copies in a consistent format.

Sources and further reading

• USP <85> Bacterial Endotoxins Test — the canonical pharmacopeial standard for endotoxin assay methodology, including LAL and rFC variants.
• USP <86> Bacterial Endotoxins Test Using Recombinant Reagents — methodology for rFC-based endotoxin detection.
• USP <621> Chromatography — general chapter covering HPLC system suitability, peak resolution, and reporting standards for chromatographic purity assays.
• USP <1226> Verification of Compendial Procedures — methodology for verifying that a stated test procedure produces the result claimed.
• ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratories — the international accreditation standard referenced on most reputable analytical-lab COAs.
• FDA Guidance: Drug Substance Chemistry, Manufacturing, and Controls Information — for regulatory context on how identity, purity, and contamination testing are documented in regulated submissions.