A method of analyzing ethylated thymidine DNA adducts is disclosed. The method comprises the steps of: providing leukocyte DNA; adding at least one isotope-labeled internal standard and a plurality of enzymes to the leukocyte DNA, and hydrolyzing the leukocyte DNA into a plurality of nucleosides; using a solid-phase extraction column to extract the plurality of nucleosides; and using a stable isotope dilution nanoflow liquid chromatography-nanospray ionization tandem mass spectrometry to detect and quantify at least one ethylated thymidine DNA adduct in the plurality of extracted nucleosides.