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Sonication: Fisher 100 - Looking for Protocol (Apr/08/2005 )

I have previously used a Branson sonicator, but recently replaced it with a Fisher 100. Does anyone have a suggested protocol for shearing crosslinked DNA (ChIP) into 500-2000 bp fragments? Also, I've been playing with the settings, and seem to get foaming randomly at both low and high settings. I'm using 7 mL glass test tubes with a 1 mL volume. Any suggestions??? Thanks!


I use Fisher 550. If you still got foaming at low settings, the only other thing that you have to be careful is to dip the tip all the way to the bottom of the tube and keep it there during sonication. You can do a test using different settings such as starting from 10X10" to 15X10" and stopping for 5-10" between each action.