Hi Sam, I believe that the Qiagen spin column miniprep kits max out at ~40kb due to the membrane of the spin column. I have isolated a ~200kb plasmid from Agrobacterium tumefaciens using the alkaline lysis method (use freshly made solutions for best yield).

Dear Sam,

I emphasize my colleague Philips answer.

lyse and neutralize your plasmids using kits reagents then take the supernatant and perform phenol chloroform extraction followed by ethanol precipitation and get pure DNA extracted of any size.