60 ÷ 2.5 = 24 mg/mL. Concentration is vial content divided by diluent volume, so 60 mg of peptide in 2.5 mL of bacteriostatic water gives 24 mg/mL. On a U-100 barrel one unit is 0.01 mL, so one unit of this solution carries 0.24 mg — 240 µg. That is the number to write on the label, because you will not reconstruct it from memory at an awkward moment.
Stated carefully, the answer depends on what you want your measurement resolution to be, and that is a real trade-off rather than a preference. More diluent gives you more syringe marks per dose and therefore less rounding error; it also gives you a larger volume to keep cold and a longer period over which the solution has to remain within specification.
Room temperature before drawing is worth the ten minutes. Cold solution is more viscous, draws slower, and is more likely to pull a bubble past the plunger seal.
Reading a lyophilised cake
| Appearance | Interpretation | Action |
|---|
| Intact opaque puck, proud of base | Cycle ran correctly | Proceed |
| Slumped to one side | Shipped before fully dry, or vibration | Usually usable; note it |
| Glassy translucent film | Collapse above glass transition | Test before use |
| Melt-back ring at stopper | Thermal excursion in transit | Test before use |
| No visible cake at all | Very low fill, or nothing there | Weigh it; query the supplier |
The underlying point is that a 0.22 µm syringe filter will remove particulates and organisms, and it will also adsorb a fraction of your peptide.
Published data on syringe dead space in the context of injection-equipment programmes quantifies low-dead-space designs as retaining under 2 µL against 35 µL or more.
One limitation: technique reduces risk, it does not remove it.
Do the arithmetic twice, ideally with someone else doing it independently.
2Small correction: the units in the third paragraph should be micrograms, not milligrams. – Dr_Bram_Verhoeven 10 months ago 3This should be linked from the help pages. – swab_and_wait 39 days ago add a comment