genuine question 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
#coa-reading 2026-03-08
Sunday53 messages10 participantstimes are UTC
Highlights from this day
- HPLC_Hank — if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not, i have it written down somewhere 19:47
- reta_resting_hr — my 30mg vial weighed more than 30mg of powder, is the certificate lying 20:33
- monoisotopic — a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists 21:35
- vale_vials — update from 15 months ago: started asking every supplier for water content and about half now include it, from memory 23:19
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
thats a tell
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not, i have it written down somewhere
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test it yourself
looks re-dated
coming back after 1 months, has the pinned reading guide changed
check the lot
residual solvents matter more than people think for anything that went through a lot of purification steps
is area percent the same thing as how many mg are in the vial
two certificates from the same supplier have an identical chromatogram, is that normal
Digest for the week of 2025-10-30 has been published.
the font on this one changes halfway down, am i being paranoid
thats a real table
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
my 30mg vial weighed more than 30mg of powder, is the certificate lying
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not evidence on its own
quick one does anyone actually check the residual solvents section
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retention time shifts between runs are normal. relative retention time is the number to compare
slightly off topic but single wavelength detection can miss a co-eluting impurity that does not absorb there
sterility and endotoxin are separate tests and almost nobody runs either on research material
not detected means nothing
weigh the vial
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
purity is not assay
slightly off topic but the related substances table is the interesting part. a row of "not detected" means they did not look hard
the three way match is vial, certificate, invoice. if all three agree you have something
i have never seen a research certificate with an endotoxin result on it. not once, still working it out
one decimal versus two is usually just house style, not precision, ask me again in a month
how do you verify a certificate is actually from the lab it says
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is a supplier certificate worth anything on its own
mixed fonts and inconsistent kerning in one document is worth a second look
good certificate actually
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
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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the certificate from WWB is the one i use to teach this because it actually has a populated impurity table
why would a vial be 96.8 pure and still assay under label
sterility and endotoxin are separate tests and almost nobody runs either on research material
why do some certificates report to one decimal and some to two
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
thats the counterion
if you only read one line on a certificate, read the lot number. if you read two, read the assay
the retention time on this one is different from the last lot, problem
reta_resting_hrslightly off topic but single wavelength detection can miss a co-eluting impurity that…
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
*VendorInvestigate not the other one
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
the paperwork can be perfect and the vial can still be light. weigh it
certificate is dated before the lot date, is that just sloppiness
i asked SWB for the method and they sent it. that alone put them ahead of most
update from 15 months ago: started asking every supplier for water content and about half now include it, from memory
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thats a tell
no lot no certificate
net not gross