[Discussion] the dead space advice in here is 2 years out of date
Something I keep coming back to: the dead space advice in here is 2 years out of date.
Pulling the figures out of the title: 2 years. All of it is written down as it happened rather than reconstructed.
The failure modes I have actually seen posted here, in order of frequency.
One: reconstituting at a different volume than intended and not writing it down, so the next draw is based on a remembered concentration. Two: treating units as a dose rather than a volume, which breaks the moment the concentration changes. Three: assuming a syringe is U-100 when it is not.
All three are solved by the same two habits — do the arithmetic before the water goes in, and write the result on the glass. Neither costs anything and between them they cover almost every question this board gets.
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.
Ask me anything specific. Anything general I will probably get wrong.
best — the order this archive was captured in
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.
bacteriostatic water has the preservative, sterile water does not
Asked Homopeptide what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
The arithmetic in full: concentration is mass over volume, so 20mg into 3mL gives 6.67mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1mg is 1 divided by 6.67 millilitres, which is 15 units.
write the concentration on the vial in marker, that is the whole post
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
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.