Guanidine and ethanol, both introduced during the prep, can reduce the A260/A230 ratio. Following the protocol will ensure these components are removed. Additionally, though unlikely, some particulates may elute which can affect the ratio as well. If this is the case, an additional 15-second spin of the eluted DNA before evaluation by spectrometry (Nanodrop®) should help. Withdrawing the DNA sample from the top of the sample can help to avoid transferring any particulates.