Abstract: The mass spectra of sixty samples of aromatic acids and their derivatives with different types of structures were determined under DEP condition by using Finnigan-MAT 4510 model mass spectrometer. It is observed that the adduct ions such as M+ArCO~+ and M+Ar~+ were produced by some species. In this paper, the conditions, regularity and mechanism of the ion-molecule association reactions have been explored in detail, and the significance of the reaction is also described.