dna quantification and quality assesement - abs 260nm / abs 280 nm <0.5 (Sep/06/2009 )

Hi,

I am using Qiagen DNA mini spin colom method and my absorbance ratio at abs 260nm / abs 280 nm is <0.5. Any suggestions please?

Thank you

Are you purifying PCR or plasmid or doing gel extraction?

I have just had problems with my readings, so I just ran some out on a gel and estimated that way. Just run it alongside a known quantity of another sample, or a ladder that you know the exact amounts in each band etc.

It turned out one of my samples was way off from the spec reading. Apparently it's not very accurate if you have quite a low concentration of DNA anyway.