The temperature dependence of the formation of negative ions from chlorinated phenols was studied. For all compounds, Cl- was produced and the intensity of the chloride ion increased with the increasing number of Cl atoms present in the molecule. For some of them, (M - HCl)(-), (M - H)(-), and M- (M: parent molecule) were also observed. The intensities of the fragment ions such as Cl- and (M - HCl)(-), increased with the increasing temperature, though that of the parent anion decreased. There may be two mechanisms to produce (M - HCl)(-). One is the HCl elimination of the hydroxylic hydrogen atom and the ortho-Cl atom. The other is the HCl elimination followed by the migration of the hydroxylic hydrogen atom to the ortho position for the 3,4- and 3,5-dichlorophenols. The branching ratio of [(M - HCl)(-)]/[Cl-] depends on the length of the H-Cl bond of the intermediate for the former mechanism. (C) 2004 Elsevier B.V. All rights reserved.