QIAfilter Plasmid Midi Kit (25)

This anion-exchange-based midi kit from QIAGEN enables fast purification of transfection-grade plasmid or cosmid DNA using a manual filtration workflow. The system is designed for culture volumes of 25–50 ml and supports high-copy, low-copy, and cosmid plasmid types, making it suitable for applications ranging from cloning to transfection and sequencing.

The kit combines QIAfilter Midi Cartridges, which use a syringe format to clear bacterial lysates by filtration in place of centrifugation, with prepacked QIAGEN-tips containing QIAGEN's proprietary anion-exchange resin. Lysates are pushed through the filter in seconds, and the cleared flow-through is loaded onto the gravity-flow tip where plasmid DNA binds under low-salt, pH-controlled conditions. A medium-salt wash removes RNA, proteins, metabolites, and other low-molecular-weight impurities, and ultrapure plasmid DNA is eluted in high-salt buffer. The DNA is then concentrated and desalted by isopropanol precipitation and collected by centrifugation.

Time per run is 110 minutes, with yields of up to 100 µg of high-copy plasmid DNA. The resin's separation properties yield DNA of purity equivalent or superior to two successive rounds of CsCl gradient centrifugation, and the workflow avoids phenol, chloroform, ethidium bromide, and CsCl, minimizing hazard to the user and the environment.