How to read a certificate of analysis

A certificate of analysis is a laboratory’s record of what it measured in one specific lot of material, on one specific day. That is all it is. It is not a licence, not an endorsement of the seller, and not a promise that the next lot will look the same. Read as a measurement with a date attached, it is genuinely useful. Read as a badge, it is worthless — which is exactly how most of this industry uses it.

The header block

Everything above the results table exists so the report can be tied to a physical vial and checked by someone who was not there.

• Task number. The laboratory’s own reference for that submission. Without it there is nothing to verify against. A certificate presented as a photograph with the task number cropped out is not a certificate.
• Client. Who paid for the test. In a supply chain this is frequently the manufacturer or an upstream distributor rather than the shop selling to you. That is ordinary and not by itself a problem. What matters is whether the seller tells you so before you notice it yourself.
• Manufacturer. Who produced the lot.
• Batch or lot code. The one field that connects the paper to the vial. If the lot code on the report does not match the lot code you were shipped, the report describes someone else’s material.
• Dates. Usually three: when testing was ordered, when the sample reached the laboratory, and when the analysis was run. A long gap between the second and third is normal; laboratories batch their work.

Content and purity are not the same number

This is the single most commonly confused pair on a peptide certificate, and the confusion is usually profitable for whoever is selling.

Content is how much of the target compound is in the vial, in milligrams. It answers “did I get what I paid for”.

Purity is what fraction of the material that is there is the target sequence rather than something else. It answers “is what I got clean”.

The two are independent. A vial can be 99.8% pure and contain 6 mg where 10 mg was expected. It can also contain a generous 12 mg of something only 90% pure. A listing that advertises “99% purity” and says nothing about content has told you about one of these and stayed silent on the other.

Why three figures instead of one

A thorough report gives three content values because three separate vials from the same lot were assayed. What you learn from that is fill consistency. Three numbers within a percent or two of each other means the filling line was behaving. One number substantially out of line with the other two — say 23.8, 24.3 and 29.3 mg — means it was not, and you should expect vial-to-vial variation across the whole lot.

A single figure is not a red flag on its own; some tests are ordered against one vial. It simply tells you less.

What an HPLC purity figure does not measure

Chromatographic purity is normally reported as area percent: the target peak’s share of the total peak area detected at one wavelength. Three consequences follow, and none of them are obvious from the number itself.

• Anything that does not absorb at that wavelength is invisible. Residual salts, water and the counterion left over from synthesis do not show up as impurity peaks. A peptide can read 99% pure by area and still be a meaningful fraction non-peptide by weight.
• Area percent is not mass percent. Different molecules absorb differently, so peak area is a proxy, not a weight.
• Purity is not identity. A clean single peak says the material is one thing. It does not say it is the right thing. Confirming identity needs mass spectrometry or a reference standard comparison, which is why a report that names the compound and quantifies it against a standard is worth more than one that only reports a percentage.

Blends are several analytes, not one

A vial containing more than one compound cannot have a single purity figure, and any seller quoting one for a blend is quoting something that does not exist. An honest report on a blend quantifies each component separately — four masses for a four-component blend — because the components differ in molecular weight and in how they behave on the column. Without per-component figures, the ratio in the vial is an assumption carried over from the weighing step.

Endotoxin is a different test entirely

Endotoxin analysis is ordered separately, appears on its own report with its own task number, and measures bacterial endotoxin — a structural component of gram-negative bacterial cell walls that survives conditions which would kill the bacteria themselves. It is reported in endotoxin units, either per vial or per milligram; the two are not interchangeable, and per-vial figures on a 60 mg vial and a 10 mg vial are not comparable.

A low endotoxin figure means low bacterial contamination. It does not mean the material is sterile, and it says nothing about suitability for use in any living organism. Treat it as one more purity metric, which is what it is.

Check the report yourself

Reputable laboratories publish a verification page: you enter the task number and the key printed on the report, and the laboratory’s own records come back. A report you cannot check independently is a picture of a report. Whatever is on the page, the laboratory’s copy is the authority.

What should make you stop

• A certificate with no task number, or no way to verify it against the laboratory.
• A lot code on the report that does not match the lot code you were sent.
• A purity percentage with no content figure anywhere.
• One certificate presented as covering every lot of a product, indefinitely.
• A single purity number quoted for a multi-component blend.
• A product photograph or a generic image used where a certificate should be.
• Any laboratory report described in terms of safety, sterility or fitness for use in humans. A laboratory measures; it does not licence.

Research use only

Everything in this catalog is supplied for in-vitro laboratory research and analytical reference use by qualified professionals. These materials are not drugs, dietary supplements or cosmetics, are not intended for human or veterinary use or for diagnostic purposes, and nothing on this page describes an effect in humans.