I'm trying to sonicate chromatin from Raw cells (mouse monocytes) that were fixated with 1% formaldehyde. I'm following the Covaris TruChIP protocol for shearing and either get no shearing or shearing with fragments size of ~500 bp.
My parameters:
duty cycle: 5 / 10%
cycles per burst: 175/200
peak incident: 104 watt
time: 3/4/6/8/ min.
I've tried combinations of all the above parameters.