#coa-reading 2025-10-13

Monday40 messages10 participantstimes are UTC

Highlights from this day

blank_run — one way your 8.9 happens with nobody lying to you 22:11
deadspace — it means the paperwork describes chemistry and not safety 23:08
ferrous_ash — and that is where we leave it. nobody here is going to tell you what to do with a non-sterile research powder 23:58

noct.titrate 21:20

thats a tell

*that should say weekly

VialBotbot21:25

Batch lookup F-1330: 6 independent reports on file, earliest 2025-03-22.

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coa_or_cope 21:29

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

follow up sterility and endotoxin are separate tests and almost nobody runs either on research material, not advice obviously

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

noct.titrate 21:37

what does net peptide content mean next to gross mass

cross_border_cam 21:38

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

[edited]

the honest summary is that a certificate tells you what the supplier says about a lot they chose to test

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for the archive tfa or acetate, how do i tell from the paperwork
mixed fonts and inconsistent kerning in one document is worth a second look

cat_on_the_tray 21:50

result back. 10mg label, assay 8.9mg, purity 99.1. vendor says that is within spec and i do not know if they are fobbing me off

blank_runlab21:51

what does the COA say for water content and counterion

cat_on_the_tray 21:54

KF 5.8%. nothing about counterion

blank_runlab21:56

then some of your missing 1.1mg is water and probably a chunk more is acetate or TFA, and the vendor is not necessarily lying

question_queue 21:57

sorry, water? its a dry powder

blank_runlab22:00

lyophilised peptide is hygroscopic. 3 to 8% residual water is completely normal in a freeze-dried cake.
Karl Fischer titration is how you measure it.
if 6% of your 10mg gross is water, 9.4mg is the most peptide-plus-salt you can have before you even start.
and the vial gained more water every second the stopper was off

cat_on_the_tray 22:01

ok that is one line item accounted for

blank_runlab22:03

now counterion. peptides come off the purification as a salt. TFA salt if they used TFA in the mobile phase, acetate if they did an exchange

the salt has mass. it is not peptide

blank_runlab22:11

one way your 8.9 happens with nobody lying to you

one way it can go, all figures illustrative

gross fill weighed into vial      10.0 mg
  minus water (KF 5.8 %)          -0.58
  minus acetate counterion (~7 %)  -0.70
  = net peptide available          ~8.7 mg

assay came back                     8.9 mg

so the vial is arguably filled correctly and the
label is just quoting gross mass. nobody defrauded
you. you still get ~11 % less drug per unit than
the number on the label implies.

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cat_on_the_tray 22:14

that is genuinely useful and also infuriating

deadspace 22:21

both, yes. this is the single biggest reason for the you got shorted / no you did not arguments in #test-results

question_queue 22:28

how do i know which salt form i have

blank_runlab22:30

the COA tells you or nobody does. a good sheet says net peptide content and salt form separately. most do not

hk_hplc 22:31

GL Biochem sheets for custom synthesis do state salt form in my experience. the retail resale sheets never do

deadspace 22:32

because the retail sheet is a marketing artifact and the manufacturing sheet is a manufacturing artifact

blank_runlab22:33

and TFA specifically is worth knowing about because residual TFA is a real thing people control for in cell work. it is not inert

question_queue 22:34

does the COA cover residual solvents at all

blank_runlab22:35

sometimes. acetonitrile, DMF, methanol, TFA. by GC headspace usually. if you see a residual solvents section that vendor is doing more than the minimum

cat_on_the_tray 22:36

mine has nothing. so my sheet is purity, KF, appearance, and a lot number

blank_runlab22:52

which is a normal research-grade sheet. it is just not the sheet people imagine they are getting

hk_hplc 22:55

worth saying out loud: none of these sheets are sterility or endotoxin

blank_runlab23:04

correct and that is a separate point people conflate constantly.
HPLC purity says nothing about bacterial endotoxin.
endotoxin is its own test, a LAL assay, and sterility is another again.
a 99.5% pure powder can carry a meaningful endotoxin load.
if those tests were run they would be named on the sheet, and on hobby-market sheets they essentially never are

question_queue 23:07

so research grade means

deadspace 23:08

it means the paperwork describes chemistry and not safety

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ferrous_ashmod23:58

and that is where we leave it. nobody here is going to tell you what to do with a non-sterile research powder

👍8

cat_on_the_tray 23:58

understood. going back to the vendor with a question about salt form rather than an accusation

cat_on_the_tray result back. 10mg label, assay 8.9mg, purity 99.1. vendor says that is within spec and…

blank_runlab23:58

that is the right move and you will learn more from their answer than from the number

hk_hplc 23:58

Qingdao Sigma answered a salt form question for me in about a day. Shanghai ERP took a week and answered a different question

deadspace 23:58

logged