From 2007.igem.org

Using QIAquick kit

Add 5 volumes of Buffer PBI to 1 volume of sample.

Pipette into a QIAquick spin column(max 770 µl) and centrifuge for 60 sec at 10,000g

Discard flow-through.

Wash: add 0.75ml Buffer PE(make sure that the buffer has ethanol added to it) to column and centrifuge for 1 min

Discard flow-through & centrifuge for 1 min

Place column into clean Eppendorf tube

Add 50ul Buffer EB or water to center of membrane

Let stand at RT for 3 min

Centrifuge for 5 min.

Measure the concentration using the UV spectrophotometer.