Counter-ion form: the field almost nobody reports — one year on posts 91–120
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
The arithmetic in post #91 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.
Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.
The signature block matters more than it appears to. A named individual with a date is a different kind of document from an unsigned one, whatever the numbers say.
I have deliberately not rounded that, because the rounding is where the argument starts.
On Counter-ion form I would separate what is worth knowing from what is worth acting on. The first list is long and the second is short, and conflating them is how threads get heated.
Adding the measurement that post #95 says would settle it.
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 uncertainty is in the assumption, not in the calculation.
Collapsed as off-topic by two members at trust level 3 or above
Where I part company with post #95, and it is a narrow parting.
I read the earlier replies on Counter-ion form twice before writing this, because I had assumed the opposite and wanted to be sure I was disagreeing with what was said rather than what I expected.
Check the lot on the vial against the lot on the document before anything else. It is the cheapest check available and it is the one that catches the mismatches that matter.
Old habit: I write down the expected answer before I calculate it.
A note on how Counter-ion form gets discussed rather than on Counter-ion form itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.
Everything in post #99 holds. The case it does not cover is the one I have.
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 am confident about the direction and much less about the magnitude.
Narrowing post #103, because the general version has more than one answer.
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.
Caveat: everything above assumes the paperwork is what it says it is.
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 arithmetic on Counter-ion form is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
Adding a note of thanks rather than an opinion. I did not know most of that.
Post #107 is the version of this I will quote in future. One addition.
Check the lot on the vial against the lot on the document before anything else. It is the cheapest check available and it is the one that catches the mismatches that matter.
Answering the question post #110 raises rather than the one it answers.
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.
Adding a source would improve this post and I do not have one to hand.
Building on post #110 rather than restating it.
The number people quote for Counter-ion form is a central estimate presented without its interval, and the interval is wide enough that the estimate is nearly uninformative on its own.
Reading this Counter-ion form thread as someone who came in with a fixed view: the third and seventh replies moved me and the confident ones did not.
Narrowing post #114, because the general version has more than one answer.
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 has been discussed before and I could not find the thread, so, again.
Everything in post #112 holds. The case it does not cover is the one I have.
The signature block matters more than it appears to. A named individual with a date is a different kind of document from an unsigned one, whatever the numbers say.
What I would check first on Counter-ion form is whether the thing being measured moved or whether the way of measuring it moved. Those look identical in a graph.
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".
Posting my Counter-ion form numbers with the method attached so they can be discounted properly. Uncontrolled, unblinded, and collected by someone who wanted a particular answer.