@TiaG’s thread on freezing insulin (Insulin below freezing -- should we risk it?) makes me wonder if it would be possible to set up an experiment to figure out the freezing point for different insulins.
Does anyone have equipment that would allow us to progressively set lower freezing temperatures with precision?
I have gear to remotely measure temperature that I could send over for this experiment. I can also send insulin samples.
How can we design a controlled experiment to cool insulin in a controlled and measured manner and note at what temp it freezes? Considerably trickier than heating something in controlled manner…
What one could do is, if we have access to a well-regulated freezing cooler, set the temperature down to 32, wait a day, check if it freezes, go down to 31, wait a day, check again etc.
I have decent (not true scientific-grade though) temperature monitoring equipment.
I have a multi meter with temperature probe… good enough for our experiment. And my peltier semi conductor… but no way to regulate its cooling…
The hurdle would be the well regulated cooling mechanism
I think tracking the temp would be more important than well regulated.
Multiple experiments with poorly regulated control but well tracked temps would likely provide the same answer.
It was not solid frozen but was in a state of slush. Visibly obvious when slowly turning the vial back and forth.
I would make a general assumption that a closed (never opened) bottle of insulin would require slightly more cooling to freeze solid as opposed to unopened insulin. (Small pressure difference.)
Freezing would of course be a combination of temperature and time.
If I was to test either the heating or cooling/freezing, I would likely use a water bath in either case.
But the water baths minimum temperature before freezing solid would be 32 degrees wouldn’t it? And my hypothesis is that insulin freezes well below that… kind of a self defeating experiment
Salt ? Alcohol?
Nah - skip the salt. Not low enough.
Alcohol bath. that would definitely work. Pretty much your choice of alcohol.
So how do we get it progressively colder in a controlled and measured way?
Maybe dry ice would be helpful?
Not sure what the practical application is of finding the number. Even if you know the freezing point, you don’t know always accurately know the temperature of a hotel fridge.
The vial of insulin does not all freeze at the same temp. The freezing point is below 32. The water suspension will freeze first, followed by all the solutes - for Humalog it’s insulin lispro, glycerin, dibasic sodium phosphate, Metacresol, zinc oxide, phenol.