DNA Extraction.
Genomic DNA of HeLa cells was extracted using DNAiso Reagent (Takara Biotechnology Co.,Ltd., Dalian, China) according to the protocol recommended by the manufacture.
Yeast genomic DNA was extracted using a previously described method.29 The isolated DNA was divided
into four equal aliquots named Group Control, Group TiO2, Group Enzyme, and Group Enzymex2 (Scheme 1).
Group Control represents that the isolated genomic DNA was directly enzymatically hydrolysis and analyzed by LC-MS/MS.
Group TiO2 represents that the isolated genomic DNA was treated by TiO2-based SPE after being hydrolyzed and then was analyzed by LC-MS/MS.
Group Enzyme represents that the isolated genomic DNA was treated by the traditional enzymatic
digestion method to remove RNA contamination and then was hydrolyzed and analyzed by LC-MS/MS.
Group Enzymex2 represents that the isolated genomic DNA was treated by the traditional enzymatic digestion method twice and then hydrolyzed and analyzed by LC-MS/MS.
The detailed procedures for the treatments can be found in the following Sections.
The residual ribonucleosides and recoveries of 2′-deoxynucleosides were calculated by dividing the signal intensities of Group TiO2, Group Enzyme, or Group Enzymex2 by the corresponding signal intensity of Group Control.