The concentration of DNA was quantified by HPLC-UV analysis of dG in the enzymatic hydrolysate of DNA. The amount of DNA was calculated from the dG content by assuming that 1 mg of DNA contained 3 μmol of nucleotides and that dG accounted for 22% of the total nucleotides in DNA [36 (link)]. The experiment was conducted on a Thermo Finnigan HPLC system with a diode array detector. Gradient elution was performed using a Luna C18 column (4.6×250 mm, 5 μm in particle size, Phenomenex, Torrance, CA) eluted with deionized water (solvent A) and methanol (solvent B) at a flow rate of 0.7 mL/min. The UV signal was monitored at 254 nm. The solvent composition began at 5% B followed by linear increase to 22% B over 15 min. Then the solvent B was raised to 80% over 2 min followed by an isocratic elution for 3 min. Subsequently, the percentage of the solvent B was brought back to 5% over 2 min, followed by an equilibration for 15 min.
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