High OD260/OD280 ratio - (Jun/08/2005 )

Hi,
after doing DNA extraction, we routinely check OD260 and OD280.
The ratios of OD260 to OD280 below 1.6 are explained as contaminants such as protein and phenol in many protocols.
However, I sometimes get very high ratios over 2 instead. Can anyone tell me what may be the possible cause of high ratios?
Thanks.

hi
Make sure you are below the max absorption potential of your spectro. If your solution is too concentrated or too dilute you will get mistakes...
i think also to pH. As pH increases the 280 reading decreases. This will cause high 260/280 ratios
ionic strength- as this increases both 260 and 280 decrease not by the same amount so the 260/280 ratio increases
Finally Phenol absorbs at 264nm. Hence, this will inflate both readings but more so the 260. for this try toi check the 230 value...