You don’t have to spend much time in a research lab to learn that pipette tips have a nasty habit of stubbornly clinging to a little bead of water. Some labs go so far as wrapping everything in foil in an attempt to “keep the moisture out.”
😧 Terrible practice!
First, this is going to trap moisture in the box, assuring you wind up with wet tips. Second, steam autoclaves only work when the steam can circulate freely to heat the items. If the moist steam hasn’t reached the tips, then the dips are not sterile. Wrapping your tip boxes in an attempt to keep the tips dry will result in 1) damp tips that 2) are not sterile!
How to Autoclave Dry(er) Pipette Tips
Nine times out of ten, a few minor changes in your standard lab practice will minimize (or even eliminate) damp tips.
Four things to keep in mind:
- Don’t bother autoclaving sterile tips! If they come sterile and in a sealed pack, they are sterile; don’t beat a sterile horse.
- Use the autoclave’s dry setting. The dry cycle is very bad for liquids (the lower chamber pressure will boil off—and even boil over—some of your liquid volume), but great for producing (nearly) dry loads.
- Make sure you have good air circulation. Don’t try to keep the tips dry; embrace the purifying steam!
- Give them time! If you just let them sit in the autoclave to cool off, tips will dry on their own. You can speed this process along by transferring your tip boxes to a heated drying cabinet (or even a spare incubator set at 55ºC).
The Best Recipe for Sterilizing Pipette Tips
Provided your tips actually need to be autoclaved (remember: Never waste time sterilizing sterile packaged items), then this is a good, reliable method:
- Open the lid of the tip tray a tad—propping it up with the lid’s locking tab helps; a little tape can hold it in place—don’t wrap the box in foil!
- Run your dry cycle as normal
- Let the damp tips dry in the warm autoclave (or transfer to a drying cabinet/incubator)