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

19 months in and purity is still the thing I get wrong

COA Well Actually ×1 Slow Clap ×2 Receipts ×3

Confession thread, sort of.

I went from 2.5mg to 1.0mg much faster than I should have because the scale had stalled and I got impatient. The stall broke about 15 weeks later, at which point I had no way of knowing whether the dose increase did anything or whether it would have broken anyway.

So now I have injection-site soreness I did not need and a data point I cannot interpret. Two lessons in one.

Posting it in the hope that somebody at week 22 reads it before doing the same thing.

19,241 up / 14,360 down57% upvoted37 commentsid z5ieph2 Sep 2025

37 comments

17 in this archive, depth 6

best — the order this archive was captured in

u/dario_boateng434 points·11 months ago·edited

Asked TFC for the batch-specific COA and they sent it within six hours, full document, batch number, date, everything. That is the baseline.

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u/tidy_vialdrawer_watchOP309 points·11 months ago

Sent one vial to PeptideMeter and VendorInvestigate. 96.8% and 99.1%. Cost me more than the vial did and I would do it again.

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u/sig_figs_sammod · analytical344 points·10 months ago·edited

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

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u/tidy_vialdrawer_watchOP178 points·10 months ago

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

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u/tidy_vialdrawer_watch137 points·10 months ago·edited

This is the correct framing. The COA structure matters as much as the number.

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u/dario_vermeulen57 points·10 months ago

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

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u/coa_janitorMOD430 points·10 months ago

Flair changed to match the content. Read the sidebar before posting next time and we are square.

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u/tidy_vialdrawer_watchOP226 points·10 months ago

Inter-lab variance on this kind of assay is routinely 1–2 points. Different column, different gradient, different integration.

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u/vito_chowdhury209 points·10 months ago

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

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u/tuva_aalto328 points·10 months ago

axis labels included, always

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u/gallbladder_gary182 points·10 months ago

axis labels included, always

Counter-anecdote: opposite result, same dose. Which mostly tells us the variance is huge.

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[removed]131 points·10 months ago

[removed by moderator]

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u/yara_antonsen-35 points·10 months ago

the related substances line is where the story is

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u/yara_antonsen1 point·10 months ago

Small correction: the trial was 3 weeks, not 25. Does not change your point but people will quote it.

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u/cato_achebe117 points·10 months ago

Small correction: the trial was 22 weeks, not 19. Does not change your point but people will quote it.

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u/elodie_yilmaz534 points·10 months ago

Flair changed to match the content.

Adding to this: area percent is doing more work than the comment implies.

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u/isabela_nilsen320 points·10 months ago

purity and net content are two different numbers, same vial

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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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