#coa-reading 2026-06-09

whats the related substances table actually telling me

test it yourself

thats a tell

one decimal versus two is usually just house style, not precision

the related substances table is the interesting part. a row of "not detected" means they did not look hard

the certificate from GL Biochem is the one i use to teach this because it actually has a populated impurity table

purity is not assay

whats the minimum a certificate has to have before you take it seriously

sterility and endotoxin are separate tests and almost nobody runs either on research material

not detected means nothing

thats a real table

is endotoxin ever tested on research material

i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does, someone check my working

gross mass on a jewellery scale plus the water content is enough to catch most underfills

why do some certificates report to one decimal and some to two

looks re-dated

if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not

does anyone actually check the residual solvents section

the retention time on this one is different from the last lot, problem

purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions

certificate is dated before the lot date, is that just sloppiness

retention time shifts between runs are normal. relative retention time is the number to compare

not evidence on its own

the paperwork can be perfect and the vial can still be light. weigh it

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

net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial

check the lot

net not gross

ok so two certificates from the same supplier have an identical chromatogram, is that normal

unrelated but i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019, from memory

a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists

is area percent the same thing as how many mg are in the vial

if you only read one line on a certificate, read the lot number. if you read two, read the assay

water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, we shall see