[Meta] the concentration rule is doing its job and people should stop complaining
the concentration rule is doing its job and people should stop complaining — with the counter-argument included, because I find it fairly persuasive. Wrote the date on the vial as well as the concentration after losing track of which one was opened first. Asked MKM what volume they reconstitute to for their own…
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.
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.
Correction: that gives 5 units, not what you have written. 30mg into 3mL is 10mg/mL and the division follows from there.
The arithmetic in full: concentration is mass over volume, so 30mg into 2mL gives 15mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1.5mg is 1.5 divided by 15 millilitres, which is 10 units.
How many mg in the vial and how many mL are you adding?
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
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do the arithmetic before you reconstitute, not while holding a syringe
dead space in the needle hub is real and it is small