This procedure removes salts, enzymes, and very small DNA fragments from a sample.
1. Add 3 volumes of Buffer QX1 to 1 volume of sample (eg. if sample is 100 uL, add 300 uL of Buffer QX1).
NB. Ensure that solution is yellow in colour. If it is orange or purple, add 10 uL of 3M sodium acetate and mix to return solution to yellow colour.
2. Vortex QIAEX II for 30 sec to resuspend beads.
3. Add 10 uL of QIAEX II to sample for every 5 ug of DNA (eg. if sample contains 15 ug of DNA, add 30 uL of QIAEX II), vortex to mix.
4. Incubate sample at room temperature for 10 min, vortexing every 2 min to resuspend beads.
5. Centrifuge samples for 30 sec and remove supernatant.
6. Add 500 uL of Buffer PE to sample, centrifuge for 30 sec and discard supernatant.
7. Repeat step 6.
8. Allow pellet to air-dry for 10 to 15 minutes until it becomes white.
9. Add 20 uL of H2O to pellet, vortex to resuspend.
10. Incubate at room temperature for 5 min.
11. Centrifuge samples for 30 sec, remove supernatant to clean tube and preserve this supernatant as it contains the desalted DNA.