A certificate of analysis, usually shortened to COA, is the document a laboratory produces when it finishes testing a sample. It is a record of what was tested, how it was tested, and what the instruments reported. Reading one is mostly a matter of knowing which section answers which question.
This guide walks through the sections that appear on most certificates. Published certificates for compounds in our catalogue are on the certificates of analysis page, and each one is filed against the product and batch it belongs to.
The header: what was tested, and when
The top of a certificate identifies the sample. Expect a product or compound name, a batch or lot identifier, the date the sample was received, and the date the report was issued. The laboratory that performed the work is normally named here too.
The batch identifier is the part that matters most in practice. A certificate describes one specific batch, not a product line, so a certificate only tells you about material from that batch. If the batch on the vial does not match the batch on the certificate, the document is describing something else.
Identity: is this the compound it claims to be?
Identity testing answers a yes-or-no question. The most common method reported for peptides is mass spectrometry, usually written as MS, LC-MS or ESI-MS on the certificate. Mass spectrometry measures the mass-to-charge ratio of the molecules in the sample, which is compared against the mass expected from the compound’s molecular formula.
- Expected mass or theoretical mass — what the named compound should weigh.
- Observed mass or found mass — what the instrument measured.
- A conclusion, often written as "conforms", "consistent with" or a pass/fail flag.
An identity section does not say anything about how much of the sample is the named compound. That is a separate measurement.
Purity: how much of the sample is that compound?
Purity is normally reported from high-performance liquid chromatography, abbreviated HPLC. The technique separates the components of a sample as they pass through a column, and a detector records each component as a peak on a chromatogram. The area under the main peak, divided by the total area of all peaks, is reported as a percentage.
Two details are worth reading carefully. The first is the detection wavelength, often written as 214 nm or 220 nm, because the number is an area percentage at that wavelength rather than a measure of mass. The second is the method or gradient, which tells you the conditions the separation ran under.
Identity and purity answer different questions, and one does not substitute for the other. A sample can be the correct compound and still contain other material, and a high area percentage on its own does not confirm which compound produced the peak.
Appearance, solubility and related observations
Many certificates record physical observations alongside the instrument results: the appearance of the material, whether it dissolved as expected in a stated solvent, and sometimes a water content figure from a Karl Fischer titration. These are descriptive observations of the sample as received.
Chromatograms and spectra
A certificate often includes the raw output behind the summary numbers: an HPLC chromatogram, a mass spectrum, or both. The summary table is a reading of those figures, so the figures are what lets you check the reading. On a chromatogram, look at where the main peak sits relative to the run time and whether the baseline returns cleanly between peaks.
Signatures, dates and revisions
The foot of a certificate normally carries the name or signature of the analyst or approver, the issue date, and sometimes a revision number. A revision number above one means the document was reissued, and the current revision is the one to read.
A short checklist
- Does the batch on the certificate match the batch on the material?
- Is the compound name on the certificate the compound you expected?
- Which method produced the identity result, and which produced the purity result?
- At what wavelength was the purity percentage measured?
- What is the issue date, and is this the current revision?
Where to find certificates for PepX Research compounds
Published certificates are listed on the certificates of analysis page, filterable by product. Certificates are added as third-party testing is completed, so coverage varies by product and batch. Each compound in the catalogue links to its own certificates where they exist.
All compounds and research materials supplied by PepX Research are for laboratory and research use only. They are not for human consumption.