A checklist for reading a certificate in under two minutes — does this still hold? posts 31–56

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.

Building on post #44 rather than restating it.

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".

The disagreement above is smaller than it looks once the terms are fixed.

Post #47 put the caveat in the right place and I want to underline it.

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.

That distinction has done more work for me than anything else in this category.

Narrowing post #48, because the general version has more than one answer.

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.

If this contradicts something upthread, the upthread version may well be the better one.

Everything in post #47 holds. The case it does not cover is the one I have.

Asking for the batch record rather than the certificate is a reasonable request and the response to it is informative whichever way it goes.

Where two documents for the same lot disagree, the useful question is which was measured and which was transcribed. Most such disagreements are the second.

Adding the caveat now so it does not have to be extracted later.

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.

Answering the question post #49 raises rather than the one it answers.

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.

That is where I would start, not where I would stop.

The arithmetic in post #53 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.

This is the version I would want a new member to read first.

Thank you — that answers what I came here to find out.

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".

Reporting the observation and leaving the explanation open deliberately.