A document, not a test: what a certificate actually is

A certificate of analysis is not a test result. It is a statement, made by whoever signs it, that a defined quantity of material identified by a batch number was subjected to defined tests by defined methods and produced results within defined limits on a defined date. Every element of that sentence is load-bearing, and a document missing any of them is not a weak certificate but a different kind of object: an assertion of quality with no way back to the evidence. The Journal has read several hundred of these and the distribution is not encouraging, though the reason is more mundane than the trade’s more excitable commentary suggests.

A certificate is a document, not a test

The confusion at the root of almost every dispute about certificates is a category error. A certificate of analysis is not a measurement. It is a record asserting that measurements were made, by named methods, on identified material, on a stated date, with stated outcomes, and that somebody reviewed and released the batch on that basis. The measurements exist elsewhere: in instrument data files, in analyst notebooks, in a laboratory information system. The certificate is the summary that travels with the goods.

This distinction has a practical consequence. When the Journal wants to know whether a purity figure is sound, we do not scrutinise the certificate; we ask for the underlying laboratory report and, where possible, the chromatogram. The certificate can only tell us what somebody concluded. The chromatogram tells us what the instrument saw, and the two are separated by decisions about integration, thresholds and reporting that the certificate does not record.

It follows that a certificate’s value is almost entirely a function of whether it can be traced back to that underlying evidence. A document with a batch number, a date, a named method and a named analyst is checkable in principle even if nobody ever checks it. A document with a percentage and a logo is not checkable by anyone, including the company that issued it, and the difference between those two situations is invisible to a buyer who reads only the number.

The test table: four columns, and most certificates carry two

The body of a certificate is a table, and a complete one has four columns: the test performed, the method used, the specification applied, and the result obtained. Four columns, one row per test. That structure is not a convention peculiar to pharmaceuticals; it is what a record of controlled testing looks like in any field, because each column answers a question the other three cannot.

The method column is where the detail belongs — not the word HPLC but a method identifier, a gradient, a wavelength, a column chemistry. The specification column states what the batch had to achieve. The result column states what it did. A certificate carrying only test and result has dropped the two columns that make the result interpretable, and this is by far the commonest structural deficiency the Journal encounters.

The compendial framework for validating an analytical procedure exists precisely to establish that a stated method can discriminate what it claims to discriminate, which is why a method reference is not bureaucratic ornament but the hook on which everything else hangs.¹² A named method can be looked up, compared, criticised and repeated. An unnamed one cannot be, and a result generated by one is a number whose provenance stops at the page.

Water, counter-ion and the mass in the vial

A lyophilised peptide is not pure peptide even when it is chromatographically pure. It is a salt, usually of trifluoroacetic or acetic acid, containing residual water that a hygroscopic powder acquires readily, and sometimes residual solvent from purification. Three lines on a certificate address this and they are usually absent: water content, counter-ion identity and content, and residual solvent.

Water is determined by Karl Fischer titration or by loss on drying, and the pharmacopoeial methods for it are old, settled and inexpensive.³ A peptide containing eight per cent water by mass contains eight per cent less peptide than its label implies, and the figure is not stable: it depends on how the vial was stoppered and how long it has been open. Counter-ion content is a larger contribution still for basic peptides purified in trifluoroacetic acid, where the counter-ion fraction can reach ten to twenty per cent of total mass.⁴

Put these together and the practical statement is the one this department repeats: the nominal mass on a research vial is an upper bound on the peptide it contains, not a value. A certificate that reports purity and is silent on water and counter-ion has told you the material is clean and nothing at all about how much of it there is.

The footer: dates, signatures and the release statement

The bottom of a certificate carries the dates, the signatures and any boilerplate. A complete footer gives the date of manufacture, the date of analysis, and either a retest date or an expiry date with the convention named. It gives the name and role of the person who performed or compiled the testing, and separately of the person who reviewed and approved it. It states the storage conditions under which the stated properties hold. And it states, in a research-chemical context, the research-use-only restriction.

The two-signature convention is worth explaining because its absence is so universal here that its purpose is forgotten. Separating performance from approval is a control against a single person’s error or judgement determining a release. It is cheap, it requires no equipment, and it is the ordinary practice in every regulated laboratory. Its function is not ceremonial: it means that when a document turns out to be wrong, there is a record of who reviewed it and on what basis.

What the footer should not carry is a signature rendered as a reused image with no accompanying name. That is not evidence of anything improper on its own — scanned signature blocks are common in legitimate commerce — but it removes the one piece of information the block exists to supply, which is the identity of a person who can be asked.

The ten-minute check

Minute one: find the batch number on the certificate and find it on the vial. Not the carton. If they do not match, or the vial has no number, stop and ask the supplier what the relationship is. Minutes two and three: find the date of manufacture and the date of analysis, and compute the interval. Then compute the interval between the date of analysis and today.

Minutes four and five: read the test table and count the columns. If the specification column is missing, the results cannot be assessed. If the method column is missing or says only HPLC, the purity figure cannot be compared with anybody else’s. Minute six: check the identity line for a theoretical mass, and check whether the convention — monoisotopic or average — is stated. Minute seven: read the signature block for a name and a role.

Minutes eight to ten: list what is not there. Content, water, counter-ion, residual solvent, endotoxin, sterility. Then decide whether any of those matter for what you are doing, which is a question only the reader can answer. The exercise does not establish that a certificate is right or wrong. It establishes whether the document can be checked at all, and in the Journal’s experience roughly a third of certificates in general circulation fail before minute five. Readers who work through this and find something they cannot interpret are welcome to write to standards@compoundjournal.com.

Readers who take one habit from this piece should take the first minute of the ten-minute check. Find the batch number on the vial. Everything else on the document is a claim about a defined quantity of material, and if the vial is not identifiably part of that quantity then the rest of the page is a well-drafted statement about something else.