Reading a peptide COA: a researcher's checklist
A Certificate of Analysis is the only thing standing between a research peptide and a black box. Here's how to read every line — and what's missing when one of those lines isn't there.
If you've shopped research peptides for any length of time, you've seen the phrase "COA available." What that phrase doesn't tell you is whether the COA is for your lot, whether the assay was run by an independent laboratory, or whether the panel of tests is actually meaningful. This post walks line-by-line through what a complete research-peptide COA should contain.
1. Identification
The top of the COA should name the compound, its molecular formula, its expected molecular mass, and the lot number. The lot number is the most important identifier on the page — every other line is conditional on it. If the COA you're reading doesn't have a lot number, or has a lot number that doesn't match the QR code on the vial in your hand, stop. The document is irrelevant to your material.
2. HPLC purity
HPLC (high-performance liquid chromatography) separates the components of a sample by how strongly each component interacts with a stationary phase under flow. The output is a chromatogram with peaks; the area under your target peak, divided by the area under all peaks, gives you "purity by HPLC area %." Most reputable suppliers report ≥98% or ≥99%. We report ≥99% as a floor, but the chromatogram itself is what matters — a single peak isn't always the only peak.
What to look for: the chromatogram image (not just the number), the column conditions (C18, gradient, flow rate, detection wavelength), and the integration table.
3. Mass spectrometry confirmation
HPLC tells you the sample is pure. Mass spec tells you the sample is the right molecule. ESI-MS (electrospray ionization) is the standard method for peptide identification. The COA should report the observed [M+H]⁺ ion mass alongside the expected mass for the sequence, with deviation in ppm or Da. A mass that matches HPLC purity but differs from the expected molecular weight means you have a pure compound — that isn't the one you ordered.
4. Endotoxin (LAL)
Lyophilized peptides can carry bacterial endotoxin from manufacturing residue. The Limulus Amebocyte Lysate (LAL) assay quantifies endotoxin in EU/mg. For research material, <5 EU/mg is a defensible threshold. This line is often missing on lower-tier COAs and is one of the strongest discriminators between suppliers.
5. Residual solvents and water content
Solid-phase peptide synthesis uses organic solvents — most commonly DMF, DCM, and TFA — that are purged during lyophilization but rarely all the way to zero. A residual-solvents panel reports any leftover quantities, typically by GC-MS, against ICH Q3C limits. Water content is reported by Karl Fischer titration in % w/w. Both lines tell you the lyophilization step was done well, not in a hurry.
6. Test lab and ISO accreditation
Anyone can run an HPLC. The credibility of the result depends on who ran it. ISO 17025 is the international standard for testing-laboratory competence. A COA from an in-house lab at the manufacturer is a starting point. A COA from an independent ISO 17025-accredited lab is the standard. We use the latter, and we list the lab on every COA so you can verify their accreditation directly.
7. Date of analysis and expiration
Lyophilized peptides stored properly are stable for 24+ months. The COA should be dated; if the date is older than the published shelf life of the compound, ask for a re-assay. Pepcore Labs re-tests any lot held in storage longer than 18 months and publishes the new COA against the original lot.
What's not on a good COA
A real COA does not contain marketing language, dosing recommendations, or claims about the compound's biological effects. It is a chemical document. If a "COA" reads like a sales sheet, it isn't a COA.
If you have questions about a specific Pepcore Labs lot, email support@pepcore.co. We can send the raw chromatogram and the test lab's accreditation certificate on request.
— Pepcore Labs · Verified to spec, every lot.