QIAGEN Plasmid Midi Kit (25)

An anion-exchange kit from QIAGEN designed for gravity-flow purification of transfection-grade plasmid DNA, using prepacked QIAGEN-tips that operate by gravity flow and never run dry. The kit processes 1 sample per run by manual (gravity flow) handling in 150 min, and avoids the use of toxic substances such as phenol, chloroform, ethidium bromide, and CsCl, minimizing hazard both to the user and the environment.

For bacteria grown in LB medium, the recommended culture volume is 25 ml with a high-copy plasmid and 100 ml with a low-copy plasmid, with yields of up to 100 µg of high-copy plasmid DNA per preparation. The kit accepts high-copy, low-copy, and cosmid DNA plasmid types and is suitable for applications such as transfection, cloning, sequencing, and capillary sequencing.

In the procedure, bacterial lysates are cleared by centrifugation and loaded onto the anion-exchange tip, where plasmid DNA selectively binds under appropriate low-salt and pH conditions. RNA, proteins, metabolites, and other low-molecular-weight impurities are removed by a medium-salt wash, and pure plasmid DNA is eluted in high-salt buffer. The DNA is then concentrated and desalted by isopropanol precipitation and collected by centrifugation. The kit can be stored at room temperature (15–25°C) for up to 2 years if not otherwise stated on the label.