the units thing finally clicked for me and I want to write it down
Thinking out loud about this: the units thing finally clicked for me and I want to write it down.
If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.
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 1mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 10mg/mL on the glass before I put the cap back.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests. It is a fraction of a percent and it is dwarfed by fill tolerance.
swirl, never shake
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no preservative.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Left up and flaired Explainer — the numbers in this one check out.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Bacteriostatic or plain sterile water?
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
Disagree with the "more water is safer" framing.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
the powder cake sits at the bottom, the volume you add is the volume that counts
Aim the stream down the wall of the vial rather than into the cake. Reconstitution is a solubility problem, not a mixing problem, and mechanical shear does nothing helpful.
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.
if the maths gives you a fraction of a unit, change the concentration
I would not round that figure. At 5mg/mL a rounding error of two units is a real fraction of the intended amount.
Careful — that arithmetic is wrong. 30mg in 3mL is 10mg/mL, so 1mg draws to 10 units, not what you wrote.
label the vial with the date as well as the concentration
The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
- 1Bacteriostatic water contains benzyl alcohol as a preservative, which is…8 comments in this branch · started by u/hedda_ekstrom