Why does my DNA sample float out of the slot when loading it onto an agarose gel?

DNA fragments purified with the QIAGEN DNA Cleanup Systems, i.e., the QIAquick PCR Purification Kit, the MinElute Reaction Cleanup Kit, the QIAEX II Gel Extraction Kit etc. may float out of the loading wells of agarose gels due to residual ethanol carried over from the wash step with Buffer PE (despite the addtition of glycerol-containing loading buffer).

Use either of the following options to remove residual ethanol from the eluate:

• re-purify the sample using a QIAquick-, or MinElute column, or QIAEX II resin
• incubate the eluate at 56°C for 10 min to evaporate the ethanol
• dry down the sample in a vacuum centrifuge, and resuspend the pellet in a small volume of sterile water