To extract plasmid DNA by Alkaline lysis method you need to prepare three solutions:
Solution I - Resuspension Buffer
25 mM Tris-HCl (pH 8)
50 mM glucose
10 mM EDTA
Solution II - Denaturing Solution
0.2 N NaOH
1.0% SDS
Solution III - Renaturing Solution (Potassium Acetate)
120 mL 5M Potassium acetate
23 mL glacial acetic acid
57 mL of dH2O
Please follow the protocol given in the link below.
The addition of RNAse A is optional. You may add 5 μL of 2 mg/mL RNase A as stated in step No 15 under the sub-heading Protocol: Kit-free Alkaline Lysis Plasmid Miniprep.