sonication problem - (Aug/03/2005 )

hello!

Im doing sonication to the cells lysate in buffer EDTA + EGTA+2M tris HCL, im using 3 lysis buffer and this is the third. Strangely my lysate is turning color to the strange metallic color. This is not a sonicator problem (no body, but me have this problem) and i think not because of the buffer (without the lysate, its not turning the color), strangely the DNA after this is ok, and the metallic dirt is remaining on the colonas filter.
i dont know what is the cause to this color change and what to do to rid of the dirt!

help please!

thanks in advance

maybe the color comes from sonicator probe. Before doing sonication, you can dip the probe in 70% EtOH and turn on the pulse for a while.

I agree with bullfrog, probably comes from the probe. I had similar residue and realized that I was touching the probe to the glass beaker with ice that my sample was in, and the residue had fallen into my tube. As long as I am careful to avoid this, I have not had residue again.