A certificate of analysis is the only document that connects the label on a peptide vial to something measurable. Everything else on a product page — the name, the stated purity, the batch number — is a claim; the COA is where a laboratory either substantiates that claim or fails to. Reading one takes about two minutes once you know what each section proves, and just as importantly, what it does not.
This guide explains the two analytical methods behind a serious COA, what a figure like “≥ 99%” actually asserts, why the identity of the testing laboratory matters, and the warning signs of a certificate that should not change your confidence in anything.
A COA is a batch-specific analytical report. A laboratory receives a sample from one production batch, runs a defined set of tests on it, and records the results against acceptance criteria. Three properties make it meaningful:
Reverse-phase high-performance liquid chromatography separates the components of the sample by how strongly they interact with a column. The output is a chromatogram: retention time on the horizontal axis, detector signal on the vertical. The target peptide appears as the main peak; truncated sequences and synthesis by-products appear as smaller peaks at other retention times.
Two things on the chromatogram are worth your attention:
Peak shape is a quieter signal. A narrow, symmetrical main peak reflects a well-controlled purification; a broad or split peak suggests degradation or a mixture of closely related forms.
Mass spectrometry measures the molecular mass of the compound and compares it to the theoretical mass of the claimed sequence. If the observed mass matches within the instrument’s tolerance, the molecule in the vial is the molecule on the label. This is the test HPLC cannot perform: a chromatogram can show a sample that is 99% something without ever establishing what.
The two methods are complementary, and a credible COA carries both. High purity with no identity confirmation proves only that a dominant compound is present. Confirmed identity with no purity figure proves the right molecule is in there, in unknown company.
A purity of ≥ 99% by HPLC means that at least 99% of the chromatogram’s peak area belongs to the main peak. Two nuances keep this figure honest:
A figure of exactly “100%” deserves suspicion rather than admiration: real chromatography of a synthesized peptide essentially always resolves some trace of by-product.
A manufacturer testing its own product has an obvious conflict: the result affects whether the batch can be sold. An independent laboratory, paid the same fee whatever the numbers say, does not. That independence is the entire value of third-party testing, and it is why our batches are sent to Janoshik Analytical, an independent laboratory specializing in peptide analysis, rather than being self-certified.
Certificates are published on our Certificates of Analysis page as batches are tested. The broader testing standards behind the catalog — what we require before a batch is listed — are described on the Quality page.
Any one of these should lower your confidence in the document; several together should end it:
Find the batch number and match it to the vial. Confirm both methods are present — HPLC for purity, mass spectrometry for identity. Check the observed mass against the theoretical mass. Look at the main peak’s shape and retention time. Confirm the laboratory is named and independent, and the dates are coherent. If all six hold, the document is doing its job. The analytical background — how these molecules are synthesized and why they are analyzed this way — is on the Science page, and every product in the catalog states the purity criterion its batches must meet.
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