[Caution] research use only means research use only
research use only means research use only, and I am aware this is a minority view on this board.
The three questions to ask before ordering anything from the long tail of a catalogue.
What exactly is it — catalogue number or sequence, not a common name, because several common names map to more than one molecule. How was identity established — mass against theoretical, ideally, rather than a bare purity figure. What are the storage conditions, stated specifically, with a state and a duration attached.
Then two commercial questions that save time: is this a stocked line or made to order, and what is the lead time in writing. All five are one email, and the shape of the reply tells you a great deal before any material moves.
Why purity and net content diverge, and why that is usually honest.
Purity by area percent is a relative measure of what the detector saw. Net peptide content subtracts counterion, water and residual solvent from the powder mass. For some compounds in this catalogue the gap between the two is large.
A vial can therefore be 99% pure and contain considerably less peptide by mass than the label weight suggests, with nothing wrong anywhere. The problem is not the chemistry; it is that people compare a purity figure from one supplier with a net content figure from another and conclude something about both. Ask which number you are being shown, every time.
On the thin testing history in this board, and what to do about it.
Most of the compounds discussed here have a handful of independent results across the entire site, and several have none. That is a fact about how few members have paid for testing, not a judgement about the material.
What follows: buy small, test identity first for anything unusual, and post the result even when it is unremarkable. The vendor source pages are built from exactly these submissions, and the compounds with the thinnest coverage are the ones where one more entry changes the picture most. Research material is not approved for human use, so what this board can usefully build is an analytical record.
Research-use-only material is not approved for human use and nothing here should be read as a recommendation to use it.
best — the order this archive was captured in
Net peptide content accounts for counterion, water and residual solvent. On some of these compounds the gap between purity and net content is substantial and entirely honest.
What reference standard was the assay run against?
What reference standard was the assay run against?
Agreed — and the naming problem is worse than most people here realise.
Storage conditions came back specific rather than generic when I asked. That told me somebody had actually done stability work.
catalogue depth is not the same as catalogue quality
That result is an area percent from an unspecified method, which is not the same as the identity confirmation being discussed.
That result is an area percent from an unspecified method, which is not the same as the identity confirmation being discussed.
Disagreeing with this bit: handling for one compound does not transfer to another by default.
purity methods differ between compound classes
Push back: handling advice from one compound does not transfer to another just because both are peptides.
Push back: handling advice from one compound does not transfer to another just because both are peptides.
Adding the practical question — stocked or made to order, and what is the lead time.
identity before purity, every time, for anything unusual
Push back: handling advice from one compound does not transfer to another just because both are peptides.
This is the rule for anything unusual. Identity before anything else.
- 1Net peptide content accounts for counterion, water and residual solvent. On…8 comments in this branch · started by u/ahmed_fonseca