Help with ChIP!

Hi everyone. I am trying to optimise the sonication part of ChIP, using probe sonicator. The lane with 0 is without sonication but still I am getting the band near 1.2 kb. I don’t get it. Also with 15, 20…30 cycles of sonication I am getting smear from 700-150bp. I have tried less than that also, but I found 15 cycles better. But I am not getting clean thick band around 250-500bp as shown in some protocol as ideal sonication. Any suggestions?

Hi everyone. I am trying to optimise the sonication part of ChIP, using probe sonicator. The lane with 0 is without sonication but still I am getting the band near 1.2 kb. I don’t get it. Also with 15, 20…30 cycles of sonication I am getting smear from 700-150bp. I have tried less than that also, but I found 15 cycles better. But I am not getting clean thick band around 250-500bp as shown in some protocol as ideal sonication. Any suggestions?