A Certificate of Analysis (CoA) is an independent lab’s report on a specific batch (lot) of a compound. It typically answers two separate questions: identity (is this actually the molecule it’s labeled as?) and purity (how much of the vial is the target compound versus other material). These are tested with different instruments, and it’s worth knowing both exist — a sample can be “pure” in the sense of having very little contamination while still failing an identity check if it’s actually the wrong compound entirely.

Purity is usually measured by HPLC (high-performance liquid chromatography), which separates a sample into its component substances and measures how much of each is present, expressed as a percentage of the total peak area. A “≥98% purity” result means roughly 98% of the detected material is the target compound, with the rest being residual solvents, synthesis byproducts, or related peptide fragments. Higher isn’t always dramatically more meaningful past a certain point — the more important thing is that the number comes from a real, dated chromatogram, not just a claim on a label.

Mass spectrometry confirms identity by measuring the molecular weight of the sample and comparing it to the expected mass of the target compound. This is what actually verifies “this vial contains BPC-157” rather than just “this vial contains something purified.” A CoA that only reports purity without an identity confirmation is telling you less than it might appear to.

Testing performed by the seller’s own in-house lab isn’t inherently untrustworthy, but it doesn’t carry the same weight as testing performed by an independent laboratory with no financial stake in the result. Third-party CoAs are one of the only practical ways researchers outside a manufacturing facility can verify what they’re actually working with. Stack Science publishes independent-lab CoAs for its products in the CoA Library as each batch completes testing.