#coa-reading 2025-09-20

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

good certificate actually

quick one is sterility tested as part of a normal purity certificate
if you only read one line on a certificate, read the lot number. if you read two, read the assay

mixed fonts and inconsistent kerning in one document is worth a second look, still working it out

is water content normally on a certificate or do you have to ask

purity is not assay

no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration

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

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

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

coming back after 17 months, has the pinned reading guide changed

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

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

test it yourself

thats a tell

is there a standard layout or does every lab do their own

single wavelength detection can miss a co-eluting impurity that does not absorb there

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

net not gross

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

a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully

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

i have never seen a research certificate with an endotoxin result on it. not once, someone check my working

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

update from 11 months ago: started asking every supplier for water content and about half now include it

tfa or acetate, how do i tell from the paperwork

an identical chromatogram on two different lots is the single biggest tell there is

residual solvents matter more than people think for anything that went through a lot of purification steps

not evidence on its own

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

tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance

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

sorry to jump in the three way match is vial, certificate, invoice. if all three agree you have something

Assay note: JEEP lot A-2601 reported at 98.1% of label content.

weigh the vial

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

how do you verify a certificate is actually from the lab it says

sorry to jump in the certificate from CPC is the one i use to teach this because it actually has a populated impurity table