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Histogram from Nanodrop - (Apr/08/2010 )

I have a question about the histogram of absorption vs wavelength i get when i nanodrop my dna samples.

What does it mean if i have a decline instead of just one peak at 260nm?
What does it mean if i have two peaks close together, like around 230nm and 260nm? does this mean that there are salts in addition to my dna? how can i get rid of them if so?


1) Decline would mean that the peak of your DNA at 260nm is overlayed by the larger peak from the contaminants at 230nm. This phenomenon is often observed when doing gel purifications. I would rather check the concentration on an agarose gel ...never trust a spectrophotometer :o

2) The large 230nm peak is often due to carbohydrates, phenol or chaotropic agents used in various kits can get rid of these traces by additional washing steps.