H there,,

We are trying to isolate E.coli plasmid DNA using the Qiagen kit. However since two times we are encountering very high genomic DNA contamination in our preps. We have checked the storage condition of reagents. Could anybdoy give any solution for this problem????

The usual problem is excessive shearing of DNA after addition of the lysis buffer P2 or neutralization buffer N3. Be more gentle with the prep at this stage. Overloading the columns and failure to clear the lysate during the post N3 centrifuge step can also cause a problem. Most likely you are using too many cells.