Direct extraction of double-stranded DNA into ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and its quantification

Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), as a green solvent, was successfully used for the direct extraction of dsDNA. The extraction efficiency and the distribution coefficient values indicated that trace amounts of DNA at the levels of < 5 ng mu L-1 facilitate quantitative fast extraction, while proteins and metal species do not interfere. A total of 30% of the DNA in ionic liquid at similar to 20 ng mu L-1 was back extracted into aqueous phase in phosphate-citrate buffer with a single-stage extraction. The extraction is demonstrated to be endothermic with an enthalpy of 34.3 kJ moL(-1). The extraction mechanisms were proposed and verified by P-31 NMR and FT-IR spectra. Interactions between cationic 1-butyl-3-methylimidazolium (Bmim(+)) and P-O bonds of phosphate groups in the DNA strands take place both in the dissolved BmimPF(6) in aqueous phase and at the interface of the two phases. This interaction consequently led to the transformation of DNA conformations, along with a reduction of ethidium resonance light scattering at 510 nm, and a procedure for DNA quantification in ionic liquid was developed based on this observation.