NA concentration estimation

[JackBean]

Hi,
what is the meaning of ratio A260/A230? I have actually never used it, only the A260/A280, where I know, it must be higher than 1.7, to be pure nucleic acid, w/o proteins.

[TaintedCherub]

It can be a few things. I found it quite hard to get full information on, but I remember reading that a 260/230 peak can represent phenol (as phenolate ion), guanidium hydrochloride and some other salts. Carbohydrate contamination also affects this ratio - glycogen coprecipitate can show a 230nm peak. My batch of GlycoBlue also has a slight contribution at 260 nm.

Word of warning - I had low 260/230 values often after gel extractions (0.5-1.0), with DNA at around 20 ng/ul by nanodrop estimation. When I ran what I thought was 200 ng of this DNA on a gel I saw absolutely nothing. Nanodrops seem to give false positives sometimes. I have talked to other people who confirmed this.

[JackBean]

Well, so should be the A260/A230 ratio high or low?