Dicarboxylic degradation products of nonylphenol polyethoxylates: Determination and structural elucidation in water samples by solid-phase extraction and gas chromatography-mass spectrometry after methylation

Abstract

A reliable method combining solid-phase extraction, derivatization and gas chromatography-chemical ionization mass spectrometry (GC-CI-MS) was developed for the measurement, in river and sewage effluent water, of four select model compounds of dicarboxylic metabolites (dm-CA 5–8P1EC) and other dicarboxylic metabolites (CA 5–8P1ECs) of nonylphenol polyethoxylates. These selected isomers were referred as dm-CA 5–8P1ECs because they have an α,α-dimethyl configuration (expressed as “dm”), five to eight C atoms and a carboxyl group in the alkyl chain, and an ethoxy acetic acid group. The derivatization of terminal carboxyl groups was successful with (trimethylsilyl)diazomethane. The best extraction conditions were obtained using an Oasis HLB cartridge as a sorbent bed and 4 ml of MTBE/methanol (9:1, v/v) elution mixture. The method detection limits of 0.03–0.07 μg/l for dm-CA 5–8P1ECs were attained in 500 ml pure water. The recovery was then evaluated for pure water, river and sewage effluent water samples. The high recoveries of typically >89% for each isomer indicated the high performance of the method. Although dm-CA 5–8P1ECs were not detected in the collected water samples, 21 isomers of CA 5–8P1ECs were identified by CI-MS and the tentative structures of six out of them were elucidated, mainly limited to the branch at α-C atom, by studying the EI-mass spectra. The relative concentrations of individual CA 5–8P1EC metabolites were calculated based on dm-CA 5–8P1ECs. The results showed that the main degradation on the nonyl chain occurred via the elimination of two carbon-units and the concentrations in Japan were much lower than those in Taiwan and Italy.