Electrochemical incineration of 4-chlorophenol and the identification of products and intermediates by mass spectrometry

This report summarizes results obtained as part of a larger effort to demon strate the applicability of electrolytic procedures for the direct anodic ( oxidative) degradation of toxic organic wastes. We refer to this process as "electrochemical incineration" (ECI) because the ultimate degradation prod ucts, e.g., carbon dioxide, are equivalent to those achieved by thermal inc ineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal ox ide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of solub le supporting electrolyte. Liquid chromatography (LC), including reverse ph ase and ion exchange chromatography, is coupled with electrospray mass spec trometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GCMS) and measurements of pH, chemical oxygen demand (COD), and total orga nic carbon (TOC), to study the reaction and identify the intermediate produ cts from the ECI of Q-chlorophenol. Twenty-six intermediate products are id entified and reported. The most abundant of these products are benzoquinone , 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorg anic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solut ion that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC w ith 98% of the original chlorine remaining in the specified inorganic forms . LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb an d 4 ppm for these intermediate products. Elemental analysis of the electrol yzed solutions by inductively coupled plasma mass spectrometry ICP-MS showe d that only trace amounts (<25 ppb) of the metallic elements comprising the metal oxide film were present in the solution.