Structural elucidation of dicarboxylated metabolites of nonylphenol polyethoxylate surfactants in surface waters by gas chromatography/tandem mass spectrometry

Persistent dicarboxylated metabolites of nonylphenol polyethoxylates (NPEOs ), carboxyalkylphenoxy ethoxy carboxylates (CAPECs), have periodically been detected during gas chromatography/mass spectrometry (GC/MS) characterizat ion of NPEO metabolites in samples of surface water and sewage effluent. An electron impact ionization (EI) MS study was conducted on two esterified C APEC metabolites, CA(4)P1EC isomers (where A(4) denotes a 4-carbonalkyl gro up plus one carboxylic group (C)). The most abundant characteristic ions we re produced by benzylic cleavages to yield [M-87](+) and [M-101](+) ions, c orresponding to ions of m/z 249 and 235, each of which is formed from one o f two isomeric dipropyl esters CA4P1EC. These two base-peak ions were selec ted as precursor ions to help elucidate the fragmentation mechanisms and su pport the proposed structures via tandem mass spectrometric (MS/MS) experim ents. The two isomers have been tentatively identified as 4-(2-ethyl-2-meth ylacetic acid)phenoxyacetic acid and 4-(3,3-dimethylpropionic acid)phenoxy acetic acid, which give rise to the fragments at m/z 249 and 235, respectiv ely. Copyright (C) 2001 John Wiley & Sons, Ltd.