Phthalic acid ester plasticizers, such as dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, dinonyl phthalate, didecyl phthalate, diundecyl phthalate, and ditridecyl phthalate were examined by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF). Phthalic Acid Esters (PAEs) can be fragmented with relative low collision energy from 4 to 15 eV. The fragment ions of the protonated PAEs were created by the loss of fatty alcoholic or alkene groups.