HPLC chromatograms of DNA films, hydrated to Γ = 2.5 H2O/nucleotide, X-irradiated at RT and then dissolved in nuclease free water. Unaltered free bases were detected by absorbance, A, at 254 nm after passing through a reverse-phase column. Uracil, U, was used as an internal standard for the purpose of quantification.15 In Cper, there is a fast-running contaminant, X, that increased the retention time for the released bases.