The invention relates to a modified spin column for the isolation and purification of plasmid DNA. A pre-filtration disc is included in a traditional spin column. During plasmid DNA isolation, the lysate can be loaded directly to the modified spin column, eliminates the need to first remove the flocculants containing cellular debris. This results in a much shortened process. Variation of the invention includes a depth filter in between the pre-filtration disc and the main separation matrix. Also provided are kits for isolation of plasmid DNA including the modified spin columns.