check the lot
#coa-reading 2026-03-15
Sunday44 messages10 participantstimes are UTC
Highlights from this day
- reship_rita — two certificates from the same supplier have an identical chromatogram, is that normal 19:25
- fasting_insulin — does anyone actually check the residual solvents section 19:30
- fasting_insulin — a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully 19:45
looks re-dated
quick one the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
thats a real table
good certificate actually
one decimal versus two is usually just house style, not precision
sloppy not sinister
not detected means nothing
gross mass on a jewellery scale plus the water content is enough to catch most underfills, someone check my working
🙏8
test it yourself
[edited]two certificates from the same supplier have an identical chromatogram, is that normal
😂7📉15👀1
purity is not assay
unrelated but retention time shifts between runs are normal. relative retention time is the number to compare
the three way match is vial, certificate, invoice. if all three agree you have something
does anyone actually check the residual solvents section
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 substancethats the counterion
certificate is dated before the lot date, is that just sloppiness
single wavelength detection can miss a co-eluting impurity that does not absorb there
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
🧪11📉1😂1
same chromatogram
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
slightly off topic but does purity by hplc at one wavelength miss things
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
mixed fonts and inconsistent kerning in one document is worth a second look, your mileage will differ
for the archive if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
[edited]net not gross
why would a vial be 98.1 pure and still assay under label
update from 17 months ago: started asking every supplier for water content and about half now include it
is water content normally on a certificate or do you have to ask
sorry to jump in 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, thats just me
residual solvents matter more than people think for anything that went through a lot of purification steps
ask for water content
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
thats a tell
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
the three way match is vial, certificate, invoice. if all three agree you have something
the related substances table is the interesting part. a row of "not detected" means they did not look hard
mixed fonts and inconsistent kerning in one document is worth a second look
🙏9❤️1
i asked JEEP for the method and they sent it. that alone put them ahead of most, i have it written down somewhere
slightly off topic but no lot number on this certificate, does that make it worthless
🎉1
coming back to this the certificate from QST is the one i use to teach this because it actually has a populated impurity table
🤝3
an identical chromatogram on two different lots is the single biggest tell there is
not evidence on its own
my 40mg vial weighed more than 20mg of powder, is the certificate lying
slightly off topic but is a supplier certificate worth anything on its own
the paperwork can be perfect and the vial can still be light. weigh it, happy to be corrected