Accepted answer
Nobody has published a cycle count, and at 2 mg/mL the concentration tells you what a wrong guess costs: a 0.1 mL aliquot holds 0.2 mg and every microlitre is 2 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 2 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 2 mg/mL and the date, and never thaw a container you will refreeze.
The short version: aliquot before freezing, thaw slowly, never refreeze a thawed aliquot, and count your cycles.
Let a frozen vial reach room temperature before opening it. Opening a cold vial in humid air condenses water into the cake, which raises residual moisture and undoes what lyophilisation achieved.
During freezing, solutes are excluded from the ice lattice and concentrate into the residual liquid. Local concentrations can rise many-fold, which promotes aggregation independently of temperature.
Selective crystallisation of sodium phosphate buffer components producing large pH shifts on freezing is a classical result in the lyophilisation literature.
The number of tolerable cycles is sequence- and formulation-dependent and no general number is honest.
Count cycles, not degrees. The cycle is the damaging event.
edited 28 Nov 2024 by harriet_lonsdale — expanded the table to cover the lower concentration