What the document actually is
A certificate of analysis (COA) reports the results of analytical tests run on a single production lot. It is not a statement about a product line, a brand, or a supplier, it is a statement about the material in one batch, on one date, by one laboratory. Two vials with different lot numbers need two certificates.
The fields worth checking
HPLC purity: what the percentage means
High-performance liquid chromatography separates the components of a sample over time. The detector produces a trace, each component appears as a peak, and purity is normally reported as the area percent of the main peak relative to the total area of all detected peaks.
Two consequences follow, and both matter. First, area percent is a relative measure, it describes the proportion of what the detector saw, not the absolute mass of material in the vial. Anything that does not absorb at the detection wavelength does not appear in the denominator. Second, the number depends on the method: a different column, gradient or wavelength can move it. That is why the method line belongs on the certificate, and why comparing a purity figure across two labs with two methods is a soft comparison at best.
Read the trace if it is included. A single dominant peak with a flat baseline is a different picture from a dominant peak flanked by shoulders, even when both round to the same headline percentage.
Mass spectrometry: identity, not quantity
Purity tells you how much of the sample is one thing. It does not tell you which thing. Mass spectrometry closes that gap: the instrument reports the mass-to-charge ratio of the ionised sample, and the certificate compares the observed mass against the theoretical mass calculated from the sequence. Identity is confirmed when the observed value falls inside the stated tolerance.
Purity without identity, and identity without purity, are each half a document. A lot can be 99% one compound that is not the compound named on the label; a lot can be correctly identified and still be half the mass of something else. Look for both.
Verified versus pending
On this catalog those two words have fixed meanings, and the storefront reads them from the same record the warehouse does:
- Verified, a certificate for that lot is on file. The purity figure, the lot identifier and the method shown on the product page are transcribed from it.
- Pending, the lot is listed, but no certificate is filed yet. In that state the product page prints the word “pending” and no number. An unverified figure is worse than no figure, so we do not display one.
Matching the paperwork to the vial
The check takes ten seconds and it is the only one that cannot be skipped: read the lot number printed on the vial label, read the lot number on the certificate, confirm they are the same string. A certificate for a neighbouring lot, a previous production run, or an unnamed “representative batch” is not evidence about the vial in your hand.
Signals that a certificate is incomplete
- No lot number, or a lot number that does not appear on the vial.
- No date of analysis.
- No named laboratory, or a lab that is not independent of the seller.
- A purity percentage with no method, no wavelength and no trace.
- An identity claim with no observed and theoretical mass to compare.
- One certificate presented as covering every lot of a product.
What to record
Log the lot number, the date the material arrived, the certificate’s date of analysis, the reported purity and method, and where the vial is stored. When a question comes up months later, that row is the answer, and it is the row an audit will ask for.
Storage and handling of the material itself is covered in storage and handling of lyophilized peptides.