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c/coa·posted 11 months ago by u/purity_pedant

[Question] how do you actually verify area percent

Question Long Haul ×2 Cold Box ×1

Right, the COA question again, but with numbers this time.

I have 5 data points over 26 weeks. The pattern is consistent enough that I do not think it is chance, and boring enough that nobody is going to screenshot it, which is usually a good sign.

The thing I would flag for anyone new: the effect I am describing showed up at week 61, not week 15. People give up long before the interesting part.

Interested in whether this matches other people's logs or whether I am an outlier.

2,521 up / 406 down86% upvoted20 commentsid 1tydg75 Aug 2025

20 comments

16 in this archive, depth 6

best — the order this archive was captured in

u/coa_collectorMOD320 points·11 months ago

This is an urgent-care question wearing a forum question's clothes. Please contact a clinician rather than waiting for replies.

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u/vito_chowdhury71 points·11 months ago

I am going to push back on this slightly.

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u/milos_trevino248 points·11 months ago

Did they give you the chromatogram or just the summary line?

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[deleted]102 points·11 months ago

[deleted]

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u/chidi_demir192 points·11 months ago

The evidence standard in c/vendorvetting gets called too strict about once a month, and every time, the thread ends with the complainant agreeing.

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u/amara_halonen156 points·11 months ago

the related substances line is where the story is

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u/wanjiru_varga-13 points·11 months ago

Disagree but this is the good kind of wrong — it is specific enough to be checked.

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u/priya_palacios0 points·11 months ago

axis labels included, always

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u/purity_pedantanalytical1 point·11 months ago

the counterion is part of the mass you paid for

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u/yannick_haddad1 point·11 months ago

post the whole document, not the headline number

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u/katrin_girard1 point·11 months ago

chromatogram or it did not happen

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u/karma_irrelevant1 point·11 months ago

Yeah, 96.8% area is not the problem, the missing impurity breakdown is the problem.

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u/kavya_verhoeven96 points·11 months ago

The chromatogram trace is where the real information lives. The summary number is just a headline.

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u/anya_moreau68 points·11 months ago

Dead space in the needle hub holds a small but non-trivial volume. On low-volume draws that can be several units.

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u/aurel_boateng19 points·11 months ago

the batch number or it did not happen

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About c/coa

How to read a certificate of analysis and what it does and does not tell you. Area% versus mass%, identity versus quantity, water content, related substances, acetate counterions, and the difference between a vendor-supplied COA and an independent test on the vial you actually received.

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