QIAGEN Plasmid Midi Kit (100)

This gravity-flow kit from QIAGEN uses anion-exchange tips to purify transfection-grade plasmid DNA from bacterial cultures. The workflow relies on centrifugation for lysate clearing and isopropanol precipitation, with the cleared lysate loaded onto a QIAGEN-tip 100 where plasmid DNA binds selectively 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 unique anion-exchange resin in QIAGEN-tips delivers DNA purity equivalent or superior to that obtained by two successive rounds of CsCl gradient centrifugation, while avoiding toxic substances such as phenol, chloroform, ethidium bromide, and CsCl. Prepacked QIAGEN-tips operate by gravity flow and never run dry, minimizing hands-on time.

The kit supports a culture volume range of 25–100 ml and handles high-copy, low-copy, and cosmid plasmid DNA. Each run processes one sample in approximately 150 min, with up to 100 µg of high-copy plasmid DNA recovered (yield depending on plasmid copy number, size of insert, host strain, and culture medium). Plasmid DNA prepared this way is suitable for applications such as transfection, cloning, sequencing, capillary sequencing, and in vitro transcription. The kit and its buffers can be stored at room temperature (15–25°C) for up to 2 years if not otherwise stated on the label.