What a certificate commits its issuer to — one year on posts 31–60
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
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.
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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.
I would want to see it done twice before believing it once.
Post #35 answers the question as asked. The question underneath it is different.
Residual solvent screening is not standard on these documents and its presence is a signal about the manufacturer's own systems rather than about the vial.
Reading it back, the second half matters more than the first.
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.
If the premise is wrong, everything after it is decoration.
Post #40 answers the question as asked. The question underneath it is different.
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.
I would be glad to be shown a cleaner way of putting this.
Collapsed as off-topic by two members at trust level 3 or above
I came in to disagree and I am leaving without a disagreement.
Worth separating two things that post #42 runs together.
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".
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.
The reasoning is more useful than the number, which is why I have shown it.
Taking post #44 at face value and following it one step further.
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.
Post #46 and I disagree about the size of the effect, not about the direction.
Counter-ion form is crucial: peptides are isolated as salts, most often trifluoroacetate from reversed-phase purification or acetate after salt exchange. The counter-ion is part of the mass in the vial and is not part of the peptide. Two vials of the same purity, one as TFA and one as acetate, contain different amounts of peptide per milligram.
I checked the source rather than the summary, and they differ.
Answering the question post #46 raises rather than the one it answers.
"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.
The arithmetic in post #49 is right; the assumption feeding it is the part to check.
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.
Posted with less confidence than the sentence structure implies.
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.
Endotoxin testing is separate: a certificate of purity says nothing about endotoxin. A chemically pure preparation can carry a clinically significant endotoxin load. If endotoxin matters, it needs to be tested and reported.
Everything in post #53 holds. The case it does not cover is the one I have.
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.
I would put this at better than even and not much better.
Narrowing post #53, because the general version has more than one answer.
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.
Old habit: I write down the expected answer before I calculate it.
A certificate 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.
I have said this before in a thread nobody could find, so it is worth repeating.
The fields that make one usable: lot identifier matching the container, test date, method identification specific enough to reproduce, the result as a number, and the acceptance criterion stated separately from the result.
The uncertainty is in the assumption, not in the calculation.