The effects of pH and salts on nucleic acid partitioning during phenol extraction

The partitioning of nucleic acids is sensitive to pH during phenol extraction. However, the exact effects of pH on phenol extraction had not been systematically investigated, and the mechanism of which were not fully elucidated. In this paper, we showed that the partitioning of nucleic acids was determined neither solely by the pH of the aqueous buffer being used, nor by the “pH of the phenol”; the latter is a completely wrong conception. We demonstrated that a key determinant for nucleic acid partitioning during phenol extraction was the equilibrated pH of the aqueous phase, which should be defined as the pH of phenol extraction. For example, when 50 mM NaAc-HAc buffer at pH of 3.47 was mixed with an equal volume of water-saturated phenol, the equilibrated pH of aqueous phase would be raised to ∼3.84. At this pH, almost all of genomic DNA partitioned into the phenol phase, and genomic DNA-free total RNA was retained in the aqueous phase. Several salts were found affecting the partitioning of nucleic acids during phenol extraction in different manners. Based on these results, a low-cost and efficient method for genomic DNA-free total RNA extraction was developed.