does purity by hplc at one wavelength miss things
#coa-reading 2025-11-24
Monday38 messages10 participantstimes are UTC
Highlights from this day
- wick_weighs — the certificate from WWB is the one i use to teach this because it actually has a populated impurity table 21:29
- deamidation — i asked JEEP for the method and they sent it. that alone put them ahead of most, take that with a pinch of salt 21:38
- VialBot — New independent result logged — TFC, lot C-4402, purity 99.2% (Medutest). 21:41
- ida_injects — tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance, ill dig out the number 21:56
- ida_injects — a vial can be 99.4% pure and hold 8.1mg of a 10mg label. both numbers are true and only one of them is the one you care about 22:56
should a certificate say which instrument and method they used
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
what does net peptide content mean next to gross mass
a vial can be 99.4% pure and hold 8.1mg of a 10mg label. both numbers are true and only one of them is the one you care about
my 15mg vial weighed more than 2mg of powder, is the certificate lying
sorry to jump in no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration, ill dig out the number
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
one decimal versus two is usually just house style, not precision
thats a tell
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
certificate is dated before the lot date, is that just sloppiness
good certificate actually
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if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
two certificates from the same supplier have an identical chromatogram, is that normal
follow up gross mass on a jewellery scale plus the water content is enough to catch most underfills
thats a real table
fridge-thermometer.png
800 × 800 · 670 KB · not retained in the public archive
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
the certificate from WWB is the one i use to teach this because it actually has a populated impurity table
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
i asked JEEP for the method and they sent it. that alone put them ahead of most, take that with a pinch of salt
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New independent result logged — TFC, lot C-4402, purity 99.2% (Medutest).
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purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
coming back to this i have never seen a research certificate with an endotoxin result on it. not once
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance, ill dig out the number
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single wavelength detection can miss a co-eluting impurity that does not absorb there
residual solvents matter more than people think for anything that went through a lot of purification steps
mixed fonts and inconsistent kerning in one document is worth a second look
a certificate should name the method, the instrument, the column and the operator. most name none of those
unrelated but the paperwork can be perfect and the vial can still be light. weigh it, from memory
the retention time on this one is different from the last lot, problem
looks re-dated
same chromatogram
slightly off topic but is endotoxin ever tested on research material
update on the earlier thing update from 4 months ago: started asking every supplier for water content and about half now include it
not evidence on its own
ask for water content
coming back after 26 months, has the pinned reading guide changed
a vial can be 99.4% pure and hold 8.1mg of a 10mg label. both numbers are true and only one of them is the one you care about
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test it yourself
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why would a vial be 98.1 pure and still assay under label