Accepted answer
Stated carefully, the distinction that resolves most of these questions is understanding what concentration actually means and why it is not the same as label claim.
Breaking it down further: if a 10 mg vial has 96.5 per cent content, you have 9.65 mg of peptide. Divide that by 2.00 mL and your concentration is 4.825 mg/mL, not 5.00 mg/mL, which is a 3.5 per cent systematic error in every dose calculation.
It helps to be literal here: number of stopper piercings matters less than the gauge doing the piercing. A 30G or 31G needle through a butyl stopper leaves a track that reseals; a 21G or 18G drawing needle punches a core and can drop it into the solution.
The Arrhenius relationship for drawing kinetics means that cold solution takes noticeably longer to draw than room-temperature solution.
One qualification: if your arithmetic and someone else's disagree by a factor of ten, one of you has made a unit error, and writing out the units at every step is the diagnostic.
If in doubt, use more diluent and accept the shorter usable window.
8This should probably be in the site help pages rather than buried in an answer. – Dr_Bram_Verhoeven 10 months ago Good answer, but the confidence interval in the cited trial is wider than implied. – nils_karlberg 2 months ago add a comment