Setup, so nobody has to ask: 20 mg · 2 mL · bacteriostatic water.
I have worked this out and I would like someone to find the error, because I suspect there is one.
My working so far, for the record, is below, and I am fairly sure the error is in the unit conversion rather than the algebra.
Is my approach right even if my number is wrong?
20 ÷ 2 = 10 mg/mL. Concentration is vial content divided by diluent volume, so 20 mg of peptide in 2 mL of bacteriostatic water gives 10 mg/mL. On a U-100 barrel one unit is 0.01 mL, so one unit of this solution carries 0.1 mg — 100 µg. That is the number to write on the label, because you will not reconstruct it from memory at an awkward moment.
To be exact about it, this is not exotic. It is just the difference between doing it deliberately and doing it approximately.
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.
| Vial | Diluent | Concentration | 0.25 mg | 0.5 mg | 1 mg | 2.5 mg |
|---|---|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 5 u | 10 u | 20 u | 50 u |
| 5 mg | 2 mL | 2.5 mg/mL | 10 u | 20 u | 40 u | 100 u |
| 10 mg | 1 mL | 10 mg/mL | 2.5 u | 5 u | 10 u | 25 u |
| 10 mg | 2 mL | 5 mg/mL | 5 u | 10 u | 20 u | 50 u |
| 10 mg | 3 mL | 3.33 mg/mL | 7.5 u | 15 u | 30 u | 75 u |
Units are U-100 insulin units, where 1 unit = 0.01 mL. Divide dose by concentration for millilitres, then multiply by 100.
Check the barrel marking, not your memory of it.
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.
I would flag the obvious failure mode: people get the concentration right, get the volume right, and then read the syringe against the wrong scale.
None of this is exotic. It is just the difference between doing it deliberately and doing it approximately.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemRead the cake before you touch the vial. An intact, opaque, evenly distributed puck that sits proud of the vial base is what a good lyophilisation cycle produces. Anything else — collapse, melt-back at the stopper, a glassy film, a cake that has slumped to one side — is evidence about the cycle, the shipping, or both.
Do not use the same needle to pierce the stopper and to administer.
If the material arrived warm and it was lyophilised, test it and proceed on the result.
The practical summary: fine gauge, gentle swirl, diluent down the wall, room temperature before drawing, and check the syringe scale.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.