does purity by hplc at one wavelength miss things
#coa-reading 2026-03-28
Saturday53 messages10 participantstimes are UTC
Highlights from this day
- lipase_lore — whats the related substances table actually telling me 18:08
- VialBot — Assay note: BCH lot F-1330 reported at 97.4% of label content. 18:37
- LC_MS_Lena — sterility and endotoxin are separate tests and almost nobody runs either on research material 19:40
- LC_MS_Lena — the certificate from MKM is the one i use to teach this because it actually has a populated impurity table 19:48
i have never seen a research certificate with an endotoxin result on it. not once
if you only read one line on a certificate, read the lot number. if you read two, read the assay, someone check my working
i asked MKM for the method and they sent it. that alone put them ahead of most
purity is not assay
is there a standard layout or does every lab do their own
the retention time on this one is different from the last lot, problem
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
while im here the paperwork can be perfect and the vial can still be light. weigh it
does anyone actually check the residual solvents section
is sterility tested as part of a normal purity certificate
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
gross mass on a jewellery scale plus the water content is enough to catch most underfills
mixed fonts and inconsistent kerning in one document is worth a second look
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
what does net peptide content mean next to gross mass
whats the related substances table actually telling me
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the three way match is vial, certificate, invoice. if all three agree you have something, ymmv
single wavelength detection can miss a co-eluting impurity that does not absorb there
tfa or acetate, how do i tell from the paperwork
thats a tell
Assay note: BCH lot F-1330 reported at 97.4% of label content.
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a certificate should name the method, the instrument, the column and the operator. most name none of those
one decimal versus two is usually just house style, not precision
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
an identical chromatogram on two different lots is the single biggest tell there is
check the lot
thats the counterion
good certificate actually
is water content normally on a certificate or do you have to ask
right so water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
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sterility and endotoxin are separate tests and almost nobody runs either on research material
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*PeptideMeter not the other one
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
the certificate from MKM is the one i use to teach this because it actually has a populated impurity table
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sorry to jump in the related substances table is the interesting part. a row of "not detected" means they did not look hard
the three way match is vial, certificate, invoice. if all three agree you have something
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
the font on this one changes halfway down, am i being paranoid
whats the minimum a certificate has to have before you take it seriously
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, your mileage will differ
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ask for water content
not detected means nothing
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
update from 4 months ago: started asking every supplier for water content and about half now include it
Reminder set. I will post here in 7 days.
good certificate actually
retention time shifts between runs are normal. relative retention time is the number to compare, n of 1 obviously
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not evidence on its own
sloppy not sinister
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
no lot number on this certificate, does that make it worthless