When a supplier hands you a Certificate of Analysis, it can look like an overwhelming grid of numbers, abbreviations, and method codes. Most guides written for this document approach it from a chemist's standpoint — they assume you know what an HPLC chromatogram is, why retention time matters, or what the difference is between a mass spectrometer and a molecular weight calculation. You are probably not a chemist. You are a Canadian buyer who wants to know whether the batch you are about to purchase is what the label says it is, at the purity claimed.

This guide translates each COA field into a plain-language buyer question. For each field we explain what the test measures, what an acceptable result looks like, what a suspicious result looks like, and what to do if the field is absent entirely.

Prerequisite: Before reading a COA, confirm that it was issued by an independent, accredited laboratory — not by the supplier itself. A COA issued by the same entity selling you the product is marketing, not verification. The lab accreditation question is covered in the ISO/IEC 17025 section below.

Field 1 — The Lot or Batch Number

COA field · Identity anchor

Lot number / Batch number

The lot or batch number is the single most important piece of information on a COA, because it is the link between the document and the physical product you receive. Every other number on the sheet is meaningless if it does not correspond to the specific lot in your vial.

What to check: Before accepting any other information on the COA, confirm that the lot number on the document matches the lot number printed on your product packaging or vial label. If those numbers do not match, you are reading the wrong COA — possibly from a different batch entirely, or from a generic certificate that the supplier uses for multiple products.

Buyer question to ask: "Is this COA specific to the lot I will receive? Can you confirm the lot number?" A reliable supplier should be able to answer immediately and unambiguously.

Pass: lot number present and matches product label No lot number = generic certificate — do not accept

Field 2 — HPLC Purity

COA field · Purity measurement

Purity by HPLC (High-Performance Liquid Chromatography)

HPLC is the standard analytical method for measuring the purity of a peptide preparation. The technique separates the components of a sample by passing them through a column at high pressure; each compound travels at a different rate (its retention time), producing a distinct peak on the resulting chromatogram. The area under the main peak, expressed as a percentage of all peak areas, is the purity figure.

What the percentage tells you, as a buyer, is what fraction of the material in the vial is the stated peptide (the rest is impurities, residual solvents, truncated sequences, or degradation products). A purity of 98% means that approximately 98 of every 100 parts of the sample, by weight or peak area, is the target compound.

What counts as acceptable: For research-grade peptides, purity of 98% or higher by HPLC is the widely cited benchmark. Some compound classes — particularly longer-chain peptides — are more difficult to synthesise at high purity, and 95–97% may be normal; the COA should note the compound name and method clearly enough for you to assess context.

What the COA must include beyond the number: A trustworthy HPLC result does not stop at a percentage. It should include the wavelength at which the measurement was taken (typically 220 nm for peptide bonds), the column type used, and ideally the chromatogram itself — the actual peak graph — either embedded in the document or available on request. Without the chromatogram, the purity figure is unverifiable.

Pass: ≥98%, method stated, chromatogram attached or available No chromatogram = unverifiable — request it before paying

Field 3 — LC-MS Identity Confirmation

COA field · Identity confirmation

Identity by LC-MS (Liquid Chromatography–Mass Spectrometry)

HPLC purity tells you how pure the sample is; LC-MS tells you what the main compound actually is. These are not the same question. HPLC could show you a beautifully clean 98% pure peak — for the wrong molecule entirely. LC-MS resolves this by measuring the molecular mass of the compound and matching it against the expected mass of the named peptide.

Each peptide has a predictable molecular weight based on its amino acid sequence and any modifications (acetylation, amidation, disulfide bonds, etc.). LC-MS fragments the molecule and measures the resulting ion masses. A result reported as "Confirmed" means the measured mass matches the theoretical mass of the stated compound within acceptable instrument tolerance.

What to look for on the COA: The field should state the compound name, the theoretical molecular weight, and either the observed m/z (mass-to-charge ratio) values or a simple "Confirmed" notation alongside the measured mass. A COA that says only "Confirmed" without reporting the observed mass provides less transparency but is still meaningfully better than no identity test at all.

Why both tests together matter: HPLC + LC-MS is the standard pairing because they answer complementary questions. A COA with only HPLC and no LC-MS cannot confirm you have the right molecule. A COA with only LC-MS and no HPLC cannot quantify how pure that molecule is. Both are necessary.

Pass: identity confirmed, observed mass reported, matches expected Missing LC-MS = purity without identity — incomplete COA

Field 4 — Karl Fischer Water Content

COA field · Moisture analysis

Water content by Karl Fischer titration

Peptides are typically sold as lyophilised (freeze-dried) powders. The Karl Fischer test measures how much residual moisture remains in the powder after lyophilisation. This matters for two reasons: high moisture content reduces the effective amount of peptide per milligram (affecting dosing accuracy for research purposes), and it accelerates degradation during storage.

What is typical: A well-lyophilised peptide powder generally shows water content below 8–10% by Karl Fischer. Values significantly above 10% suggest incomplete or poor lyophilisation, which affects both the stability and the effective purity of what you receive.

Is this field always present? Not always. Some COAs from lower-tier labs omit Karl Fischer results. Its absence is not a red flag in the same category as missing HPLC or LC-MS — but its presence is a positive signal that the lab performed a more comprehensive panel. High-quality research-grade material generally includes this test.

Pass: <8–10% water content Absent: note it — not a deal-breaker if HPLC/LC-MS present

Field 5 — Endotoxin Testing (LAL / Bacterial Endotoxins)

COA field · Safety indicator

Endotoxin / bacterial endotoxins by LAL (Limulus Amebocyte Lysate) test

Endotoxins are lipopolysaccharides (LPS) released from the cell walls of gram-negative bacteria. They are a common contaminant of peptides synthesised using biological precursors or produced in conditions with inadequate sterility controls. The LAL test is the standard method for measuring endotoxin levels; it uses blood cells from the horseshoe crab (Limulus polyphemus) that react visibly in the presence of endotoxins.

For the Canadian buyer, the endotoxin figure is particularly relevant for any peptide that may come into contact with biological systems. Acceptable thresholds vary by intended use; the WHO's general pharmaceutical guideline suggests thresholds in EU/mg, though specific limits depend on application.

Is this field always present? Endotoxin testing is less common on COAs from general research-peptide suppliers than HPLC or LC-MS. Its presence is a meaningful quality signal, particularly if the endotoxin level is reported below a stated threshold with the test method (gel clot or turbidimetric LAL) noted.

Pass: below stated EU/mg threshold, method noted Absent: note it — premium suppliers include it; budget suppliers often skip

Field 6 — Laboratory Accreditation (ISO/IEC 17025)

COA field · Lab credibility

ISO/IEC 17025 accreditation (or equivalent)

ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories. A laboratory accredited under this standard has had its technical competence, equipment calibration, staff qualifications, and quality management independently audited by a national accreditation body. In Canada, the relevant accreditation body is the Standards Council of Canada (SCC); in the United States, it is A2LA or NVLAP; in the United Kingdom, UKAS.

What this means for you as a buyer is simple: an ISO/IEC 17025 accredited lab has been independently verified as competent. Its results carry more weight than those from an unaccredited lab because the methodology, equipment, and traceability of measurements have been audited by a body that has no financial relationship with the lab's customers.

Where to find this on the COA: Look for the lab's accreditation number, the accrediting body name, and the accreditation scope. A reputable lab will print its accreditation certificate number on its letterhead or at the footer of the COA. You can verify the accreditation status independently through the accrediting body's public register — for example, the SCC's accredited organisations search for Canadian labs.

Pass: ISO/IEC 17025 accreditation number present, verifiable No accreditation stated: treat results with increased scepticism

What to Do When a Field Is Missing

Not every COA you receive will be complete. The response depends on which field is missing and how critical it is to the purchase decision:

A Canadian Buyer's COA Reading Sequence

When a supplier sends you a COA, work through it in this order:

  1. Find the lot number and confirm it matches your product label.
  2. Confirm the issuing lab is independent (not the supplier) and accredited (ISO/IEC 17025 or equivalent).
  3. Read the HPLC purity figure. Is it ≥98%? Is the method stated? Is the chromatogram attached or available?
  4. Read the LC-MS identity result. Is the molecule confirmed? Is the observed mass reported?
  5. Note the Karl Fischer water content if present. Is it below 10%?
  6. Note the endotoxin result if present. Is it below the stated threshold?
  7. If any of the first four steps fail, pause the purchase and ask the supplier for clarification or the missing document.

Reminder: A COA is a quality document, not a legal permit. It does not authorise the purchase or use of a compound; it describes the composition of one batch. For the regulatory and legal context relevant to buyers in Canada, see our companion guide: Legal Peptide Sourcing in Canada.

For buyers who want to go further — understanding how to verify whether a batch number is real, how to cross-reference COAs across a supplier's catalogue, and what specific red flags indicate a fabricated certificate — see our next guide: Batch and Lot Verification: What to Demand and How to Spot a Fake COA.