Guanidine thiocynate contamination in gel extraction - Precipitation vs column (May/25/2011 )

Hey, all,

I've been trying to purify a 1.1 kb fragment from an agarose gel, but I had a peak absorbance at 230 in all my samples (using the QiaQuick gel extraction kit), so I'm pretty sure I have a high amount of guanidine thiocynate contamination.

Everything I've heard on this has had people recommend Na-acetate/alcohol precipitation. Possibly stupid question, but would a PCR purification kit (like the Invitrogen PureLink) work as well?

Thanks in advance!

You can use two washes of PE buffer. That would remove any Guanidium thiocyanate from the membrane.

A PCR purification kit would work... but it will cost more and you would still need to be careful to remove all the guanidium chloride from the membrane with wash buffer. A guanidium chloride solution is used to make the DNA bind to the column silicon matrix.

NaAcetate and ethanol percipitation, followed by 70% ethanol wash would solve your problems.