(1) Bacterial cells were not lysed completely: Too many bacterial cells were used. If more than 10 A600 units of bacterial culture were used, separate them into multiple tubes. After PD3 Buffer addition, break up the precipitate by inverting to ensure higher yield. (2) Incorrect DNA Elution Step: Ensure that Elution Buffer was added and absorbed to the center of the PD Column matrix. (3) Incomplete DNA Elution: If plasmid DNA is larger than 10 Kb, use preheated Elution Buffer (60-70°C) in the Elution Step to improve the elution efficiency. (4) When a more concentrated plasmid DNA solution is desired, 30 ml of elution buffer is suggested. However, in comparison with using 50 ml of elution buffer, there is about 40% of plasmid which cannot be eluted when 30 ml are used. Therefore, no less than 30 ml of elution solution should be used. (5) If ddH2O, pH <7 is used for DNA elution, lower efficiency of plasmid elution will result.