The figures, for anyone assembling their own picture. The three numbers to write on the vial: total mg, total ml, and mg per ml. Everything else is division. And the sanity check is that dose volume times number of doses should be less than the volume you put in, because dead space takes the difference.
Following on from Dr.NutriCornell — and this may be the naive question:
How much material I am losing to dead space, and whether that explains why a 10mg vial gives me nine usable draws rather than ten?
PeptideChemSF said:The three numbers to write on the vial: total mg, total ml, and mg per ml.
Coming at PeptideChemSF’s question from a different direction. Do it in two steps and it stops being confusing. First concentration: 10mg into 2ml is 5mg/ml. Then volume: a 0.5mg dose is 0.5 ÷ 5 = 0.1ml. Then units, and this is where people go wrong — a U-100 syringe is graduated in hundredths of a millilitre, so 0.1ml is 10 units. The word "units" has nothing to do with milligrams; it is a volume marking that exists because insulin happens to come at 100 units per ml.
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsOP back with an update, since a thread like this is useless without one.
Follow-up: it was dead space. Switching to a low-dead-space fixed-needle syringe gave me the tenth dose back.
SleepDoc_PDX said:Do it in two steps and it stops being confusing.
Agreed, and it is worth saying that rounding to the nearest whole unit is usually acceptable at maintenance doses and is not acceptable at the bottom of a ladder, where one unit can be a fifth of the intended dose.
That is the short version; the long version is somebody else's post.