Autoclave Pipet tips

[John.Monahan at CIBADIAG.COM]

We are having a big discussion here as to what the proper parameters are for 
autoclaving our pipet tips. I say 15minutes at 15psi at 130degrees. Another 
person in the lab keeps changing the settings to 30 minutes at 15 psi at 120 
degrees. What is correct or what do others use? 
     
     Kristina,
     
     15 minutes seems kind of short if you are trying to "kill" all life 
     forms (eg spores), however...
     
      First, I think 15 psi of steam = 121 degrees. If you raise the 
     temperature, the pressure will go up. The preferred temperature 
     setting for the autoclave should be determined by the stability of the 
     material being autoclaved (probably isn't critical for pipet tips).  
     
     Second, the time is dependent (in part) on the how much you jam in the 
     autoclave.  The autoclave starts timing when the temperature sensor 
     reaches the set temperature. It will be some time later when the last 
     piece  of what your autoclaving reach temperature.  For example two 
     ten liter flasks with 15 liters media (combined volume) took at least 
     60 minutes with the autoclave I use. 
     
     As a Grad Student, I once autoclaved a foam bucket full of ice (a 
     small wager was at stake).  After "autoclaving" ice remained in the 
     ice bucket (autoclaved for I think 30 minutes, with a lid on the ice 
     bucket).  Uh, _ autoclaved ice, is it sterile? 
     
     Finally, What are we trying to kill when we autoclave pipet tips?  
     Bacteria? Nucleases? What autoclave conditions kill "nucleases"?  Has 
     anybody measured this?
     
     John Monahan
     john.monahan at cibadiag.com