[Discussion] the thymosin advice in here is 3 years out of date
Posting this as a discussion rather than a claim: the thymosin advice in here is 3 years out of date.
Pulling the figures out of the title: 3 years. All of it is written down as it happened rather than reconstructed.
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.
Would rather be corrected in public than confident in private.
best — the order this archive was captured in
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.
Identity confirmed, or purity only?
the less-tested the compound, the more the identity test matters
Small fix — that is net peptide content, not purity. Both are on the certificate and they differ substantially here.
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.
Asked for a catalogue number rather than removing. Common names are ambiguous here and it makes threads unusable later.
Bought small on anything without a testing history here. That rule has never once cost me anything.
Purity methods differ by compound class. A gradient and wavelength developed for one peptide will not necessarily resolve the relevant impurities of another.
Purity methods differ by compound class.
soren_osei is right that a purity figure without a method is not comparable to one with a method.
Push back: handling advice from one compound does not transfer to another just because both are peptides.
identity before purity, every time, for anything unusual
What lead time were you quoted for that line?
Correcting my own comment: the storage condition I quoted was for the lyophilised powder, not for solution.
Net peptide content on the certificate?
a mass spectrum costs little and answers the real question
Asked QSC which lines they keep in regional stock versus make to order and got a clear split. It changed what I ordered.
ask what the reference standard was
ask what the reference standard was
Disagreeing with this bit: handling for one compound does not transfer to another by default.
Stocked lines and made-to-order lines have different lead times and different storage histories. Both are ordinary; the difference is worth confirming before you commit.
Cosigning the lead-time point. Made-to-order and stocked are completely different propositions and both are legitimate.
lead times on unusual lines are the thing to confirm up front
I would not treat catalogue breadth as a quality signal. It is a business decision, not an analytical one.
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