[Lab] split one vial across VendorInvestigate and PeptideMeter — 94.2% and 96.8%
Short version of the title, which is already short: split one vial across VendorInvestigate and PeptideMeter — 94.2% and 96.8%. Longer version underneath.
Figures up front so nobody has to dig: 94.2% and 96.8%.
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.
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.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
best — the order this archive was captured in
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.
Confirmed the lead time in writing before ordering a made-to-order line. It was longer than the site suggested and entirely reasonable once explained.
Correction: that name covers two different molecules and the thread has been discussing both as one.
lyophilised and stored cold is the default for a reason
That method was developed for a different compound class and would not resolve the impurities you are asking about.
research-use-only material is not approved for human use
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
Identity confirmed, or purity only?
Small fix — that is net peptide content, not purity. Both are on the certificate and they differ substantially here.
purity methods differ between compound classes
ask what the reference standard was
ask what the reference standard was
Adding the practical question — stocked or made to order, and what is the lead time.
Has anyone here tested that compound at all?
the sequence is the product, everything else is packaging
a mass spectrum costs little and answers the real question
Right — WXT answered a handling question with actual storage conditions rather than a generic line, which is the standard.
Asked for a catalogue number rather than removing. Common names are ambiguous here and it makes threads unusable later.
Sent an unusual compound to VendorInvestigate because nobody on this site had ever posted one. 98.7% against a claimed 98.5%.
a secretagogue and a fragment are not the same class of thing
Purity methods differ by compound class. A gradient and wavelength developed for one peptide will not necessarily resolve the relevant impurities of another.
if nobody has tested it here, that is a fact about us, not the compound
- 1The three questions to ask before ordering anything from the long tail of a…10 comments in this branch · started by u/canada_coverage
- 2purity methods differ between compound classes7 comments in this branch · started by u/soren_osei