related substances — 9 things I got wrong before I got it right
The title is the argument: related substances — 9 things I got wrong before I got it right. Here is the rest of it. The PDF creation date being later than the analysis date is usually a re-issue or a re-export. It is worth one question and it is not evidence of anything on its own. Ask what the stability statement…
UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.
area% is not mass%, and the difference is the whole game
How to ask for a batch record without it turning into a negotiation.
One email, three requests: the batch-specific certificate for lot X, the method line behind it, and the storage condition the stability statement was written against. No preamble, no explanation of why you want it.
What comes back is the signal. A full document with the column and gradient printed on it, inside a day, tells you there is a real quality system behind the operation. That is the test I run before I order from anyone new, and it costs nothing.
water content is on there and everyone skips it
Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.
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Sent one vial to Medutest and VendorInvestigate. 98.2% and a claimed 98.0%. Cost me more than the vial and I would do it again.
Are the related substances itemised or is it a single total?
Are the related substances itemised or is it a single total?
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.