Gel extractions can be a low yield affair, but overnight incubation over a spin column can increase yields. This protocol details a modified QIAquick Gel Extraction protocol.
QIAquick Gel Extraction Kit
Cut the desired band out of an agarose gel using a scalpel.
Weigh the slice in a snap cap tube and add 3 volumes of QG buffer per volume of gel, assuming the gel density is roughly 1µl/mg. This can be whatever gel dissolving buffer (with chaotropic salts and guanidine thiocyanate) you typically use.
Add 1 volume of isopropanol to the tube and vortex.
Place a QIAquick spin column in a collection tube. Add the sample to the column and incubate over column overnight at room temp.
Centrifuge spin column for 1 minute at 13,000 RPM.
Discard flow through. Repeat step 5 if the sample volume was greater than 800 µl.
Add 750 µl of buffer PE to column and centrifuge for 1 minute at 13,000 RPM. Discard flow through.
Centrifuge for an additional 1 minute to remove all wash buffer.
Place column in collection tube and add 50 µl EB buffer or water directly to the silica portion of the column. Incubate up to 4 minutes then centrifuge the column for 1 minute to elute DNA.
Analyze DNA using a standard Nanodrop/general spectrophotometer protocol for 260/280 absorbance ratios. Store all samples in a -20 oC freezer.