water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
#coa-reading 2026-02-27
Friday46 messages9 participantstimes are UTC
Highlights from this day
- birch_bloods — right so purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions 12:24
- taper_or_not — a certificate should name the method, the instrument, the column and the operator. most name none of those 14:00
- assay_not_purity — sorry to jump in tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance 15:11
residual solvents matter more than people think for anything that went through a lot of purification steps
no lot no certificate
mixed fonts and inconsistent kerning in one document is worth a second look
is there a standard layout or does every lab do their own
[edited]is a supplier certificate worth anything on its own
is endotoxin ever tested on research material
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no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
what does net peptide content mean next to gross mass
one decimal versus two is usually just house style, not precision
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an identical chromatogram on two different lots is the single biggest tell there is, ask me again in a month
sloppy not sinister
while im here single wavelength detection can miss a co-eluting impurity that does not absorb there
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why would a vial be 99 pure and still assay under label
unrelated but the certificate from SGN is the one i use to teach this because it actually has a populated impurity table
while im here net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
update from 14 months ago: started asking every supplier for water content and about half now include it
right so purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
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i have never seen a research certificate with an endotoxin result on it. not once
[edited]not detected means nothing
i asked GGPeps for the method and they sent it. that alone put them ahead of most
ask for water content
slightly off topic but two certificates from the same supplier have an identical chromatogram, is that normal
update on the earlier thing the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
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sterility and endotoxin are separate tests and almost nobody runs either on research material
not evidence on its own
how do you verify a certificate is actually from the lab it says
if you only read one line on a certificate, read the lot number. if you read two, read the assay
does anyone actually check the residual solvents section
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
should a certificate say which instrument and method they used
*Medutest not the other one
a certificate should name the method, the instrument, the column and the operator. most name none of those
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thats the counterion
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i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
sorry to jump in tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
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is sterility tested as part of a normal purity certificate
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
does anyone keep a folder of certificates to compare over time
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, for what its worth
the paperwork can be perfect and the vial can still be light. weigh it
[edited]tfa or acetate, how do i tell from the paperwork
same chromatogram
fridge-temps.csv
115 rows · not retained in the public archive
certificate is dated before the lot date, is that just sloppiness
does purity by hplc at one wavelength miss things