A ratio greater than 2 in OD260/OD280 suggests what type of contamination?

A ratio greater than 2 in OD260/OD280 indicates significant RNA contamination in a sample. The OD260/OD280 ratio is a common method used to assess the purity of nucleic acids. In this context, the absorbance at 260 nm primarily correlates with nucleic acids, while the absorbance at 280 nm is indicative of proteins.

When analyzing nucleic acids, a pure sample of DNA or RNA typically has an OD260/OD280 ratio around 1.8 to 2.0. If the ratio is significantly higher than 2, it suggests that there is more RNA present in the sample than DNA or that the sample is contaminated with additional substances influencing the absorbance readings – in this case, RNA. This ratio, therefore, provides insight into the composition of the sample and highlights the presence of contaminating RNA, which can interfere with applications such as quantitative PCR or other downstream molecular biology techniques where the purity of DNA is crucial.

Other types of contamination such as protein or water typically present different absorbance characteristics, leading to lower ratios for protein contamination or unaffected ratios for water, which does not significantly interfere with the nucleic acid absorbance measurements.