Low 260/230 ratios from DNA purification question - (Sep/11/2014 )

Hi everyone,

I have been trying to purify some DNA I have extracted and subsequently linearized, but have ended up with some not so good 260/230 ratios - they are ranging from 0.55 - 0.69.  My 260/280 ratios are 1.72-1.78 which may not align with the ideal ratio of >1.8 but from a google search this seems passable for DNA (please correct me if I am wrong?).  Given these 260/230 ratios and possibly the 260/280 ratios, would it be a bad idea to continue on with my experiments (I plan to use the DNA for in vitro transcription to synthesize probes for in situ hybridization) with this 'purified' DNA?  

Also, would anyone have any advice for increasing my 260/230 ratios?  I am using phenol chlorofom isoamyl to purify my DNA. 

Many thanks in advance for any help - it is very much appreciated!

The 260:280 ratio is dependent on the solvent for the DNA, if you use water, 1.8 is the theoretical reading for pure DNA. For other solvents such as TE or even just tris based buffers, the readings should be higher.

As to your ratios, now that you have purified, you could try passing the DNA through a commercial DNA extraction column (PCR based one will usually suit, unless your plasmid is bigger than 10 kBP).