agarose electrophoresis gel has 500 bp bright smear after mini prep - (Nov/28/2014 )

Greetings

I performed a mini plasmid prep using the old conventional way (buffer p1-3, no coloumns involved) i then digested my preps and loaded onto a agarose gel. I get a bright smear that ranges from 100 bp - 500 bp, could this be impurities like salts from the buffers or something? its not the first time i use this method usually for impurities i get a faint small smear below the 100 bp marker  band.

Sounds like you either have a lot of RNA contamination or have digested some of the plasmid and genomic DNA by incubating in the alkaline buffer for too long before neutralization.