More usefully, full dissolution of a well-lyophilised cake should take under a minute with gentle swirling and no agitation. If it takes ten minutes, the cake is either over-dried, partially collapsed, or the peptide has already aggregated.
On re-freezing something that thawed in transit: if it arrived as a lyophilised solid that warmed but never got wet, re-freezing costs you nothing except the thermal cycle.
Dead space by syringe type
| Configuration | Dead volume | Loss at 5 mg/mL | Over 20 draws |
|---|
| Fixed-needle insulin syringe | 3–5 µL | 15–25 µg | 0.3–0.5 mg |
| Low-dead-space, detachable | <2 µL | <10 µg | <0.2 mg |
| Standard luer-lock + 30G | 35–60 µL | 175–300 µg | 3.5–6 mg |
| Luer-lock + 21G drawing needle | 70–100 µL | 350–500 µg | 7–10 mg |
Photograph the vial against a matte black card with a single point light source off to one side, not with a flash from the front.
The 28-day beyond-use convention for a multiple-withdrawal preserved preparation derives from USP compounding chapters, which set it on microbiological risk rather than chemical stability.
Do the arithmetic twice, ideally with someone else doing it independently.
edited 10 Jul 2026 by tare_weight — expanded the table to cover the lower concentration
The dead-space number surprised me until I did the multiplication across twenty draws. – hana_petrikova 7 months ago Thank you — the worked example is what makes this usable. – rhian_prydderch 9 months ago add a comment