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.
Buffer salts crystallise at different points during freezing. Sodium phosphate is the classic example: the dibasic form crystallises first and the pH of the residual liquid falls by several units. That pH excursion is the real damage in many cases.
Never refreeze a thawed aliquot. The whole point of aliquoting is that the aliquot is single-use, and refreezing it discards the benefit.
Selective crystallisation of sodium phosphate buffer components producing large pH shifts on freezing is a classical result in the lyophilisation literature.
Let a frozen vial reach room temperature before opening, or you condense water into it.
6Small correction: it is the number of cycles rather than the freezer temperature that does the damage. – fib4_reader 18 days ago 7This should be linked from the help pages. – RP_C18 2 months ago add a comment