Hello, I am extracting DNA from granulocytes. I firstly extracted PBMCs from fresh blood 2 weeks ago by ficoll, and the packed granulocytes in the bottom was conserved in 4℃ till today. When I am going to extract the DNA from them by DP304 （Tiangen），adding red blood cells lysis （1350ul）to 450ul packed granulocytes，mixing by a spinner at room temperature for 15 min， then centrifuge at 10,000 rpm for 3min，however, there is no white precipitate left in the tube.
I am so confused since I just did as this several weeks ago and extrated DNA，but from fresh blood.
Is it because of the packed granulocytes has been kept in 4℃ for 2 weeks？ Or have you ever come across such things and how would you deal with it？
Thank you so much！
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