Accepted answer
Nobody has published a cycle count, and at 20 mg/mL the concentration tells you what a wrong guess costs: a 0.1 mL aliquot holds 2 mg and every microlitre is 20 µg. Damage from freezing is not gradual attrition — it is concentrated at the phase transitions, where ice excludes solute and the unfrozen fraction climbs well above 20 mg/mL for as long as the transition lasts. Two slow cycles can therefore do more than four fast ones, which is why a cycle count is the wrong unit in the first place. The way to make the number one is to make it one: split at reconstitution into single-draw aliquots, label each with 20 mg/mL and the date, and never thaw a container you will refreeze.
The relevant physics is ice-front concentration: as water crystallises, everything dissolved is concentrated into the shrinking liquid phase, including buffer salts.
Never refreeze a thawed aliquot. The whole point of aliquoting is that the aliquot is single-use, and refreezing it discards the benefit.
Reported and extrapolated stability by condition
| State | Condition | Usable window | Basis |
|---|
| Lyophilised solid | −20 °C, sealed, dry | 24–36 months | Supplier guidance |
| Lyophilised solid | 2–8 °C, sealed | 12–24 months | Supplier guidance |
| Lyophilised solid | 25 °C, sealed | 4–8 weeks | Extrapolated (Arrhenius) |
| Lyophilised solid | 40 °C, sealed | 1–2 weeks | Extrapolated |
| Solution, preserved | 2–8 °C | 28 days | USP microbiological convention |
| Solution, preserved | 25 °C | 3–7 days | Extrapolated |
| Solution, unpreserved | 2–8 °C | 24 hours | USP microbiological convention |
Windows for the solid state are chemical; windows for solution are microbiological and usually shorter than the chemical limit.
Thaw slowly at room temperature or in the refrigerator rather than in warm water. Rapid warming creates local thermal and concentration gradients that promote aggregation.
Selective crystallisation of sodium phosphate buffer components producing large pH shifts on freezing is a classical result in the lyophilisation literature.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Count cycles, not degrees. The cycle is the damaging event.