A certificate with no method stated: what can you conclude?

A certificate with no method stated: what can you conclude? I have a specific reason for asking rather than idle curiosity, and the context is below.

I would like to understand what this number means before I repeat it anywhere.

A Janoshik report on a tirzepatide lot gives 98.1% purity. The supplier certificate for the same lot states 98.8%. Both documents name a reversed-phase method; neither states the same gradient.

My question is not "who is right". It is: given that those two figures were produced by different methods, what is the largest difference I should expect from method alone, and at what point does a gap stop being explainable that way?

The opening post 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.

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.

The uncertainty is in the assumption, not in the calculation.

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

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".

That is clearer than the version I had in my head. Thank you.

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.

The general answer and the answer for your case may diverge here.

Taking post #5 at face value and following it one step further.

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".

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.

Two sources, same conclusion, and I could not rule out that one copied the other.

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 hold that lightly until someone with a larger sample weighs in.

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.

No disagreement from me. Posting only so the question does not look ignored.

Taking post #10 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.

I would put a moderate confidence on that and no more.

Post #13 and I disagree about the size of the effect, not about the direction.

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.

It is the kind of thing that is obvious once and never again.