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#coa-reading
Purity is not assay. A COA without a lot number is a picture.
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What a Certificate of Analysis certifies and what it does not: HPLC area percent versus assay content, lot traceability, the related-substances table, water content by Karl Fischer, counterion content and net peptide, residual solvents, and how to spot a recycled chromatogram or a re-dated document.
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PURITY IS NOT ASSAY. Purity (area %) says what fraction of what is in the vial is the target compound. Assay says how many milligrams are actually there. A vial can be 99.4% pure and contain 8.1mg of a 10mg label.
No lot number, no COA. A document that cannot be tied to the vial in your hand is decoration.
Net peptide content is gross mass minus water and minus counterion. That is why a perfectly honest 10mg vial can weigh out at 11.4mg of powder.
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2026-06-26gross mass on a jewellery scale plus the water content is enough to catch most underfills22 msgs · 7 people2026-06-25thats a tell15 msgs · 3 people2026-06-24an identical chromatogram on two different lots is the single biggest tell there is40 msgs · 6 people2026-06-23water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it17 msgs · 6 people2026-06-21is endotoxin ever tested on research material25 msgs · 6 people2026-06-20update from 8 months ago: started asking every supplier for water content and about half now include it16 msgs · 3 people2026-06-18sterility and endotoxin are separate tests and almost nobody runs either on research material residual solvents matter…55 msgs · 12 people2026-06-16update from 13 months ago: started asking every supplier for water content and about half now include it47 msgs · 11 people2026-06-14no lot number on this certificate, does that make it worthless46 msgs · 11 people2026-06-11i asked BCH for the method and they sent it. that alone put them ahead of most59 msgs · 13 people2026-06-10slightly off topic but the related substances table is the interesting part. a row of "not detected" means they did…52 msgs · 11 people2026-06-09whats the related substances table actually telling me45 msgs · 9 people2026-06-06for the archive the three way match is vial, certificate, invoice. if all three agree you have something30 msgs · 7 people2026-06-05the certificate from WXT is the one i use to teach this because it actually has a populated impurity table25 msgs · 5 people2026-06-03if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not27 msgs · 5 people2026-06-02coming back to this does anyone actually check the residual solvents section17 msgs · 5 people2026-05-31purity is not assay54 msgs · 11 people2026-05-30an identical chromatogram on two different lots is the single biggest tell there is16 msgs · 4 people2026-05-29coming back after 4 months, has the pinned reading guide changed33 msgs · 6 people2026-05-28a certificate should name the method, the instrument, the column and the operator. most name none of those, happy to…41 msgs · 8 people2026-05-27if you only read one line on a certificate, read the lot number. if you read two, read the assay16 msgs · 3 people2026-05-26if you only read one line on a certificate, read the lot number. if you read two, read the assay16 msgs · 5 people2026-05-25the paperwork can be perfect and the vial can still be light. weigh it44 msgs · 10 people2026-05-24a certificate should name the method, the instrument, the column and the operator. most name none of those28 msgs · 6 people2026-05-21what does net peptide content mean next to gross mass19 msgs · 7 people2026-05-20ask for water content56 msgs · 9 people2026-05-19sterility and endotoxin are separate tests and almost nobody runs either on research material, i could be wrong26 msgs · 7 people2026-05-18check the lot16 msgs · 3 people2026-05-17an identical chromatogram on two different lots is the single biggest tell there is54 msgs · 9 people2026-05-15coming back after 9 months, has the pinned reading guide changed26 msgs · 8 people
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an identical chromatogram on two different lots is the2026-06-18 · 15 msgsan identical chromatogram on two different lots is the2026-05-31 · 12 msgshow to keep your own lot log without losing your mind2026-05-25 · 5 msgssingle wavelength detection can miss a co-eluting impurity that2026-05-24 · 12 msgsupdate from 16 months ago: started asking every supplier2026-05-13 · 6 msgsupdate on the earlier thing water content is why2026-04-26 · 7 msgsthe retention time on this one is different from2026-03-28 · 17 msgsa certificate should name the method, the instrument, the2026-03-21 · 8 msgsok so gross mass on a jewellery scale plus2026-03-07 · 11 msgswhats the related substances table actually telling me2026-02-25 · 17 msgsthe retention time on this one is different from2026-02-08 · 7 msgsthe three way match is vial, certificate, invoice. if2026-01-29 · 8 msgsdoes purity by hplc at one wavelength miss things2026-01-18 · 16 msgswhats the related substances table actually telling me2025-12-17 · 8 msgstwo certificates from the same supplier have an identical2025-11-16 · 17 msgsupdate from 3 months ago: started asking every supplier2025-11-10 · 12 msgsthe honest summary is that a certificate tells you2025-10-20 · 11 msgssorry to jump in the three way match is2025-10-09 · 10 msgsan identical chromatogram on two different lots is the2025-05-17 · 10 msgsnobody can authenticate a certificate from a scan. you2025-04-30 · 10 msgsthe certificate from TFC is the one i use2024-09-20 · 11 msgs