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c/coa·posted 2 years ago by u/zeynep_zielinski

the batch question that gets asked weekly, answered properly

Suspicious Cold Box ×7 Sourced ×2 Receipts ×2

Something I noticed reading old threads that I have not seen said out loud.

The advice on COA in this community changed substantially around the start of last year, and nobody went back and updated the older posts. So depending on which thread the search engine hands you, you get two contradictory answers with the same confidence.

I have listed what I think the current consensus is below. Correct me — that is the point of posting it.

8,140 up / 834 down91% upvoted62 commentsid 1y1pgo15 Mar 2024

62 comments

22 in this archive, depth 5

best — the order this archive was captured in

u/tidy_vialdrawer_watch281k points·2 years ago

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

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u/ahmed_rasmussen641 points·2 years ago

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

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u/zeynep_zielinskiOP287 points·2 years ago

Metadata check caught a COA that was created in a browser four months after the analysis date. Not evidence of fraud, but worth flagging to JEEP.

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u/zeynep_zielinskiOP149 points·2 years ago

Sent one vial to PeptideMeter and VendorInvestigate. 93.7% and 99.0%. Cost me more than the vial did and I would do it again.

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[removed]109 points·2 years ago

[removed by moderator]

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u/aurel_boateng74 points·2 years ago

Sent one vial to PeptideMeter and VendorInvestigate.

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

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u/bastian_aalto41 points·2 years ago

Water content on the document? That affects your concentration math.

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u/amira_dumitru108 points·2 years ago

axis labels included, always

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u/zaid_balogun561 points·2 years ago

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

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u/zeynep_zielinskiOP324 points·2 years ago

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

Yes, exactly this, and it is the bit that took me 8 weeks to accept.

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u/sunday_shot_sal225 points·2 years ago

Cosigning. The batch number is load-bearing information.

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u/nadia_fonseca153 points·2 years ago·edited

the batch number or it did not happen

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u/reflux_report191 points·2 years ago

the counterion is part of the mass you paid for

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u/soren_nkemelu382 points·2 years ago

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

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u/emeka_beaulieu-4 points·2 years ago

No. This is the kind of confident post that gets copied into a screenshot and repeated for years. Where is the evidence.

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u/amylin_amyamylin185 points·2 years ago

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

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u/nadia_fonseca297 points·2 years 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/dead_space_doug230 points·2 years ago

The COA I was holding said 96.8% area and I thought it was trash. Turns out the method was solid and the impurity profile was clean.

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u/emeka_chowdhury74 points·2 years ago·edited

area% is not mass%, and here is exactly why it matters

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u/teodor_lokken51 points·2 years ago

Not convinced. The evidence does not support that reading.

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u/receptor_bias_rick39 points·2 years ago

the counterion is part of the mass you paid for

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u/valeria_girard48 points·2 years ago

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

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

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c/coa rules
  1. Post the full document. Cropped COAs that hide the batch number or date get removed.
  2. Redact your own name and order id, not the vendor's batch details.
  3. No "is this good?" without saying what the compound and claimed purity are.
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