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c/coa·posted 21 days ago by u/emeka_beaulieu

[Question] vendor COA says 99.2%, my Janoshik came back 97.4%. who is wrong

Question Receipts ×4 Cold Box ×2

Genuinely asking, not being difficult.

Everyone in c/scamalerts repeats that batch is important. I believe it, but I have never seen anyone show why, and when I search I get 17 threads of people agreeing with each other.

Is there a paper? Is there a measurement? Or is this one of those things that is true because it has been repeated since 2023?

I am not trying to be the "source?" guy. I would just like a source.

3,083 up / 1,188 down72% upvoted11 commentsid 1vchro8 Jul 2026

11 comments

2 in this archive, depth 1sorted by:

best — the order this archive was captured in

u/priya_palacios0 points·20 days ago

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

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u/nadia_fonseca-36 points·20 days ago

genuinely useful, thanks

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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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130submissions

Aug 2023created

submissions / month, last year

Janoshik Analytical

Independent HPLC and mass spec. The number you get is the number they found.

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GL Biochem (Shanghai)

Custom peptides and amino acids direct from the manufacturer since 1998. ISO 9001 / cGMP. Batch COA every order.

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