[Discussion] we are measuring concentration at the wrong time and calling it noise
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 concentration is the divisor between the dose you want and the volume you draw.
So doubling the water halves the concentration and doubles the units for the same dose. Nothing is diluted in any sense that matters; you are simply reading a bigger number off the same barrel. Pick the water volume that puts your usual dose on a whole number of units and life gets easier.
The whole calculation, once, with real numbers.
You have a 5mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 1.67mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 0.75mg you need 0.75 divided by 1.67 millilitres, which is 45 units on the barrel. Write "1.67mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Please do not ask me what dose you should be on. I genuinely do not know and neither does anyone else here.
best — the order this archive was captured in
Adding more water does not change how much peptide is in the vial. It changes the concentration, which changes the volume you draw for the same amount. That is the entire relationship.
Adding more water does not change how much peptide is in the vial.
Right, and the arithmetic behind it: 10mg in 1mL is 10mg/mL, so 1.5mg is 15 units.
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.
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.
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.
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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Are you accounting for the powder volume, or is that where the confusion is?
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
This. Showing the working is the fastest way for somebody else to spot the mistake.
- 1Spent 9 weeks confused about this until somebody drew the table for me.…8 comments in this branch · started by u/alcohol_aversion