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c/coa·posted 19 days ago by u/aurel_boateng

PDF producer string says the file was made in a browser. is that normal

COA

Right, the related substances question again, but with numbers this time.

I have 19 data points over 10 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 26, not week 75. People give up long before the interesting part.

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

181 up / 56 down76% upvoted23 commentsid 1vmhdd10 Jul 2026

23 comments

17 in this archive, depth 5

best — the order this archive was captured in

u/tidy_vialdrawer_pls0 points·18 days ago

the method line is doing real work, not just window dressing

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u/certified_referenceMOD1 point·18 days ago·edited

Removed a chain here. The rule is one line long and it is not negotiable.

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u/purity_pedantanalytical0 points·18 days ago

the counterion is part of the mass you paid for

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u/laila_yilmaz9 points·19 days ago

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

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u/wrong_network_w7 points·18 days ago·edited

Batch number and date of analysis? Both are load-bearing.

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u/janek_ferrari4 points·18 days ago

no "is this good?" without saying what the compound and claimed purity are

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u/rania_okonkwo8 points·19 days ago

What were the related substances listed individually?

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u/gastric_emptying_g-14 points·19 days ago

chromatogram or it did not happen

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u/anya_correia1 point·19 days ago

chromatogram or it did not happen

Yes, exactly this, and it is the bit that took me 16 weeks to accept.

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u/janek_ferrari1 point·18 days ago

the method line is doing real work, not just window dressing

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u/alcohol_aversion1 point·18 days ago

Slight fix: the number was 98.7, not 96.8. Decimal point, but a fairly consequential one.

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u/nadia_kjaer1 point·18 days ago

Strongly agree. Mass% and area% are answering different questions on the same document.

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u/tove_ogunleye1 point·17 days ago

post the whole document, not the headline number

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[deleted]3 points·18 days ago

[deleted]

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u/dario_vermeulen1 point·18 days ago

the counterion is part of the mass you paid for

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u/spreadsheet_gremlindata6 points·18 days ago

Disagree. What you are describing is consistent with area percent, not with what you concluded.

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u/emeka_beaulieu4 points·17 days ago

Sent one vial to PeptideMeter and VendorInvestigate. 98.4% and 98.0%. Cost me more than the vial did and I would do it again.

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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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