The degradation of linear alkylbenzensulphonic acids (LAS) by means of H2O2 and O-2 as oxidant was investigated by mass spectrometry identification and characterization of partial oxidation products. Polar water-soluble compounds were analyzed by LC/MS with electrospray ionization (ESI), and the volatile products were trapped by means of headspace solid phase micro-extraction (HS-SPME) and investigated by GC/MS with El and Cl ionization. The shortening of LAS alkylic chain and the oxidation of the terminal part to carboxylic acids or the insertion of oxygen atoms to give hydroxylic derivatives, were observed. The reaction leads also to volatile aldehydes, with H2O2, and acids and lactones, with O-2. On the basis of demolition product structures a relevant difference in selectivity between H2O2 and O-2 was pointed out, obtaining important information on the reaction mechanism. (c) 2005 Elsevier B.V. All rights reserved.