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[rima]

Hi all

My problem is a little different from u guys but thought of posting since u all are discussing regarding DNA sonication.I have to sonicate dna for a viscosity measurement using sonicated dna. I used 5ml dna in Tris-HCL buffer (ph 7.5) in 50ml falcon tube for sonication using 4mm dia probe. I sonicated for 25 mins (5secs on, 10 secs off) in ice bath. I checked on gel and am getting the required size of<200bp. But after about 15mins there are some white particles in the solution. Is the dna precipitating out? the particles are not settling down with centrifugation, there is no contamination from the probe and the probe tip is not touching the tube...whats happening?