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Ampicillin solution does not frozen at -20 C. - (Feb/12/2018 )

Good night everyone, 


Here I have a question that I encountered today. 


Some time ago, I purchased a Ampicillin solution (100 mg/mL) from Sigma and put the solution in several micro-centrifuge tubes. I then stored the tubes at -20 C. One week later (today), when I was going to use the Ampicillin solution, I found that it was not frozen. The solution in the tubes was still liquid. I checked other solutions in the same freezer and found that they were all well frozen. Only the Ampicillin solution was not frozen. A long time ago, I purchased the same Ampicillin solution and stored it at -20 C. At that time, it was well frozen. Only this time, the Ampicillin solution was not frozen. 


I then transferred the Ampicillin solution to the -80 C freezer. 


My questions are: 



  1. Is this Ampicillin solution still good to use? I just need it to select bacteria, and I do not need an accurate concentration. I am sure the -20 C freezer in our lab is working as all other solutions were frozen. At least, the temperature in this freezer is less than 0 C. 
  2. For an antibiotic solution, is it safe to store it at -80 C? I mean, will the low temperature cause an issue? I saw that it is suggested that Ampicillin solution should be stored at -20 C. I am assuming that -80 C will also be good, but I am not sure.
  3. There is a similar post (, but my situation is different. The Ampicillin solution was stored at the -20 C freezer for about one week. If we assume the freezer has a temperature higher than -20 C but lower than 0 C, is my Ampicillin solution still good? Many thanks!

-Xinqing Wang-

It will be fine to use. The non-freezing probably indicates that the solution was super-cooled - give it a shake or flick and it should become solid rapidly.


Thanks a lot Global Moderators! Now, I have put the Ampicillin solution at -80 C. Will the temperature of -80 C a good choice? Thanks! 

-Xinqing Wang-

As far as I know it won't damage the Ampicillin to be stored at -80, it'll just take up space in your -80 and take a lot longer to thaw each time you want to use it