#coa-reading 2026-02-06

ask for water content

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

i have never seen a research certificate with an endotoxin result on it. not once

is sterility tested as part of a normal purity certificate

update from 16 months ago: started asking every supplier for water content and about half now include it

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

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

does anyone keep a folder of certificates to compare over time

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

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

sterility and endotoxin are separate tests and almost nobody runs either on research material, ask me again in a month

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

single wavelength detection can miss a co-eluting impurity that does not absorb there, ill dig out the number

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

not evidence on its own

same chromatogram

check the lot

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

why would a vial be 99.4 pure and still assay under label

unrelated but a certificate should name the method, the instrument, the column and the operator. most name none of those

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

a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
sterility and endotoxin are separate tests and almost nobody runs either on research material

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

net not gross

i asked GL Biochem for the method and they sent it. that alone put them ahead of most

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

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

New independent result logged — TFC, lot E-2205, purity 98.6% (Medutest).

what does net peptide content mean next to gross mass

Batch lookup F-1330: 4 independent reports on file, earliest 2025-08-04.

good certificate actually

looks re-dated

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