First of all, what are the plasmids you want to purify? Some are low copy number plasmids, so the yield will be low. You can increase the volume of overnight culture. The protocol is designed for 3 ml overnight culture. If you increase to 6 ml, then you need to double the volume of P1, P2, and P3 buffer. Alternatively, you can do it in two tubes each as described in the protocol. First load the lysate from one tube, wash with QC and elute DNA with QF. Then re-equilibrate the spin column with QBT, and process the second tube of lysate. Combine the eluted DNA and concentrate by ethanol precipitation.
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