This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
A certificate of analysis is a statement by its issuer that a defined test was performed on a defined lot and produced a defined result. That is all it is, and it is not nothing. What makes it usable: lot identifier matching the container, test date, method identification specific enough to reproduce, the actual result as a number, and the acceptance criterion stated separately from the result.
Taking post #122 at face value and following it one step further.
The failure mode on field-by-field walk through a certificate is boring rather than dramatic. It is almost always the step everyone assumes was done correctly because it is too simple to get wrong.
Post #121 and I disagree about the size of the effect, not about the direction.
Field-by-field walk through a certificate is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.
This settles it for me, at least until somebody posts a reason it should not.
"Not less than 98 per cent" is a specification. "98.3 per cent" is a result. A certificate carrying only the first has not told you what was measured.
I have separated what I observed from what I concluded, which does not always happen.
Worth separating two things that post #124 runs together.
What I can speak to on field-by-field walk through a certificate is narrow, so I will keep it narrow rather than generalising from it. Beyond that boundary I do not know.
Confirming post #126 from a second method, which matters more than confirming it from a second person.
Adding a reference point for field-by-field walk through a certificate. Mine is a single case, collected without controls, and I am posting the method alongside it so it can be discounted appropriately.
I had written a reply contradicting post #128 and deleted it. Here is what survived.
The distinction between release testing and characterisation is one industrial documents make and retail ones usually do not. It is the difference between "we tested every lot for this" and "we established this once".
It cost nothing to check and would have cost something not to.
Reading old certificates: if a certificate is dated years ago, the lot it describes might be old. That is not automatically a problem but it is worth noting. Fresh testing on the current lot is stronger than old testing on an older lot.
That is all the detail I have. Someone else will have more.
Peptide content and chromatographic purity are separate determinations and a certificate that reports only one has answered only one question. Content is the one that tells you how much is in the vial.
Post #131 put the caveat in the right place and I want to underline it.
Field-by-field walk through a certificate is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.
For anyone finding this later: the short answer on field-by-field walk through a certificate is that it depends on one thing, and the rest of the thread is people identifying which thing.
When a document puts the specification in the result column, it has told you the release criterion, not the measurement. Those are different claims and the second is weaker.
I have seen it go both ways, which is why I hedge.
A chromatogram supplied as a small image is legible for peak shape and not for baseline detail. That is enough to sanity-check an integration and not enough to reproduce it.
The short answer was in the first line; everything after is the working.
Post #135 and I disagree about the size of the effect, not about the direction.
A request rather than an answer: could whoever has the primary source for field-by-field walk through a certificate post it? I have seen the claim three times this month and each version had lost a qualifier.
Taking post #135 at face value and following it one step further.
Speaking only to field-by-field walk through a certificate as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
I read post #135 twice before replying, because I had assumed the opposite.
The distinction between release testing and characterisation is one industrial documents make and retail ones usually do not. It is the difference between "we tested every lot for this" and "we established this once".
Post #139 answers the question as asked. The question underneath it is different.
What would change my mind on field-by-field walk through a certificate is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.
The arithmetic in post #140 is right; the assumption feeding it is the part to check.
An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main peak and nothing about what it is.
Asking for the batch record rather than the certificate is a reasonable request and the response to it is informative whichever way it goes.
For what it is worth, the same held on the two occasions I checked.
Narrowing post #144, because the general version has more than one answer.
The thing about field-by-field walk through a certificate that took me longest to accept is that a plausible mechanism is not evidence of an effect. It is a reason to look, not a result.
Posting my field-by-field walk through a certificate numbers with the method attached so they can be discounted properly. Uncontrolled, unblinded, and collected by someone who wanted a particular answer.
What fields matter on a certificate: lot number matching the vial, test date, the analytical method stated specifically, the measured result as a number, and the acceptance limit stated separately. A certificate missing any of these is weaker.
Anyone with a larger sample, please post it.
No disagreement from me. Posting only so the question does not look ignored.
Amino acid analysis gives content: it hydrolyses the peptide and quantifies the residues. It measures the peptide content independent of chromatographic purity. Very few supplier certificates report it.
The claim is narrower than it sounds, and deliberately so.