test it yourself
#coa-reading 2026-04-21
Tuesday53 messages11 participantstimes are UTC
Highlights from this day
- HPLC_Hank — the honest summary is that a certificate tells you what the supplier says about a lot they chose to test 19:22
- courier_vs_post — i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019 19:27
- area_percent — retention time shifts between runs are normal. relative retention time is the number to compare 20:53
- LC_MS_Lena — an identical chromatogram on two different lots is the single biggest tell there is, still working it out 20:56
thats the counterion
is water content normally on a certificate or do you have to ask
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancenobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
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i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancenot evidence on its own
why would a vial be 97.4 pure and still assay under label
sterility and endotoxin are separate tests and almost nobody runs either on research material, ask me again in a month
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
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mixed fonts and inconsistent kerning in one document is worth a second look
i have never seen a research certificate with an endotoxin result on it. not once
ask for water content
gross mass on a jewellery scale plus the water content is enough to catch most underfills
the font on this one changes halfway down, am i being paranoid
residual solvents matter more than people think for anything that went through a lot of purification steps
thats a tell
slightly off topic but if you only read one line on a certificate, read the lot number. if you read two, read the assay
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
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
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
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purity is not assay
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial, thats just me
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
thats a real table
retention time shifts between runs are normal. relative retention time is the number to compare
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an identical chromatogram on two different lots is the single biggest tell there is, still working it out
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is sterility tested as part of a normal purity certificate
no lot no certificate
no lot number on this certificate, does that make it worthless
a certificate should name the method, the instrument, the column and the operator. most name none of those
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
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same chromatogram
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not, take that with a pinch of salt
is endotoxin ever tested on research material
[edited]does purity by hplc at one wavelength miss things
two certificates from the same supplier have an identical chromatogram, is that normal
weigh the vial
while im here the three way match is vial, certificate, invoice. if all three agree you have something
if you only read one line on a certificate, read the lot number. if you read two, read the assay
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what does net peptide content mean next to gross mass
tfa or acetate, how do i tell from the paperwork
one decimal versus two is usually just house style, not precision
check the lot
sloppy not sinister
single wavelength detection can miss a co-eluting impurity that does not absorb there
whats the minimum a certificate has to have before you take it seriously
looks re-dated
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coming back after 18 months, has the pinned reading guide changed
for the archive my 2mg vial weighed more than 10mg of powder, is the certificate lying
whats the related substances table actually telling me
is a supplier certificate worth anything on its own
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good certificate actually
the paperwork can be perfect and the vial can still be light. weigh it
not detected means nothing