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Quality and testing

A chemist explains why "99 per cent" is not a grade

Started 8 May 2026 · 12 replies · 82 hearts · read 1.2k times

WystanCheltenham, UK · 8 May 2026
2 months ago

A question rather than an update: A chemist explains why "99 per cent" is not a grade

Putting this here because I do not want to be sold anything, I want to know what is actually established.

I want to be careful about how I phrase this because I am not accusing anybody of anything. I am asking what a document actually establishes.

I am asking because two people I trust have told me opposite things and both of them cited the same study.

My question is about what a particular measurement does and does not tell you, because I think I have been reading more into it than it says.

Since I have put a figure in the title I should stand behind it: 99 per cent, exactly, and I checked before posting rather than after.

Happy to be told I have misread it. That would be the most useful possible outcome of this post.

27

SephNorwich, UK
#1

Peptide content by weight is the figure people most often assume is on a certificate and most often is not. Ask for it explicitly.

9

SunilFacilitatorBirmingham, UK
#2

Facilitator note: everything discussed in this circle is research-use-only material, which is not a formality — it was never manufactured, released or documented for use in a person.

11

TanviMumbai, IN
#3

Reading Sunil, I recognised more of that than I expected to.

What an analysis tells you is narrow and precise, and most of the confusion in this subject comes from expecting it to answer a wider question.

5me too 5

TobiasHamburg, DE
#4

Nothing to add except that I am glad this thread exists.

4

ZebAustin, TX
#5

Tanvi, thank you for that. It gives me somewhere to start from.

I sent one vial to two services because I did not trust myself to read a single result, and they agreed, and that was worth the cost.

8

FenellaCirencester, UK
#6

What I found is that two labs with different gradients can resolve a close-eluting impurity differently and give two honest, different answers.

2me too 9

PatrickLimerick, IE
#7

The certificates worth having name the method and the column chemistry. That is what let me stop second-guessing what I was reading.

6

TorKeswick, UK
#8

Something worth knowing: sterility and endotoxin are separate assays, commissioned separately, and almost nobody here has ever commissioned them.

6

YannickBrussels, BE
#9

That is a kinder way of putting it than I have managed about myself.

6me too 4

TobinCork, IE
#10

Coming back to what Tor wrote further up, because it is the bit I keep thinking about.

What helped was reading a certificate line by line with somebody who knew what each line was, which took twenty minutes and changed everything.

7

SunilFacilitatorBirmingham, UK
#11

Speaking as a facilitator: we do not name individuals in this circle and we do not accuse anybody of anything. We describe what a document does and does not show.

11

EdwynNewcastle, UK
#12

I found the guides here on reading a certificate the most useful thing on this site, and I have sent them to about a dozen people.

7