How pure does DNA have to be for next-generation sequencing (NGS)?

For next-generation sequencing, DNA should ideally have an A260/280 value of around 1.8 and an A260/230 value between 2.0 and 2.2; lower values may indicate contaminants that absorb strongly at 280 nm (mainly proteins) and 230 nm (such as organic compounds), respectively. Special attention to RNA content should also be taken, however, as RNA absorbs at the same wavelength as DNA and can increase the A260/280 or A260/230 ratios.