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c/reconstitution·submitted 4 months ago by u/julia_erdogan

[Discussion] we are measuring concentration at the wrong time and calling it noise

Discussionbranch of 8 comments

Posting this as a discussion rather than a claim: we are measuring concentration at the wrong time and calling it noise. Why "more water" keeps confusing people, including me for a month. The vial contains a fixed amount of peptide. Water changes nothing about that amount. What it changes is concentration, and…

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8 comments, started 4 months ago
u/alcohol_aversion450 points·4 months ago

Spent 9 weeks confused about this until somebody drew the table for me. 15mg, 3mL, 5mg/mL, 2mg is 40 units. That is the whole thing.

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u/iman_falk655 points·4 months ago

Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions for a person.

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u/yusuf_nakamura160 points·4 months ago

Reconstituted at 2mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 5mg/mL on the glass before I put the cap back.

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u/karl_fischer_kev54 points·4 months ago

Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.

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[removed]21 points·4 months ago

[removed by moderator]

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u/julia_erdoganOP9 points·4 months ago

Are you accounting for the powder volume, or is that where the confusion is?

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u/wanjiru_varga15 points·4 months ago

I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.

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u/sock_puppet_spotter103 points·4 months ago

This. Showing the working is the fastest way for somebody else to spot the mistake.

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About c/reconstitution

The arithmetic and the technique. Bacteriostatic versus sterile water, reconstitution volume as a concentration choice, converting mg/mL into insulin-syringe units, dead space, swirl-not-shake, stopper coring, and how long a reconstituted vial is actually good for. Math errors get corrected fast and politely.

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