Dicarboxylic degradation products of nonylphenol polyethoxylates: synthesis and identification by gas chromatography–mass spectrometry using electron and chemical ionization modes

Abstract

The synthesis, mass spectra and detectability of four selected dicarboxylic degradation products (CAPECs) of nonylphenol polyethoxylates (NPEOs) are reported. The selected isomers have an α,α-dimethyl configuration (expressed as “dm” in their abbreviation), five to eight C atoms and a carboxyl group in the alkyl chain, and a carboxymethoxy acid group (dm-CA 5–8P1ECs). The synthesis was successfully accomplished via a reaction sequence that started from anisole. After trimethylsilylation with N, O-bis(trimethylsilyl)acetamide or methylation with (trimethylsilyl)diazomethane, the derivatives of the dm-CA 5–8P1ECs were subjected to a GC–electron ionization (EI)–MS and GC–isobutane chemical ionization (CI)–MS. In EI–MS, ion peaks at m/ z = 265 and 207, corresponding to the α,α-dimethyl structures via the benzyl cleavage of carboxyalkyl chain, were the most significant ions of the trimethylsilyl and methyl derivatives, respectively. In CI–MS, the main ion peaks of dm-CA 5-, dm-CA 6-, dm-CA 7-, and dm-CA 8P1EC after methylation were at m/ z = 129, 143, 157, and 171, respectively, corresponding to the loss of methyl phenoxyacetate from [ M + H] +; meanwhile significant peaks were detected at 321, 335, 349, and 363, corresponding to the loss of the trimethylsilanol after trimethylsilylation. The potential for the identification and quantification of individual branched carboxyalkyl isomeric mixtures of CA 5-, CA 6-, CA 7-, and CA 8P1EC metabolites based on corresponding dm-CA 5–8P1ECs revealed the advantage of the GC–CI–MS although the detection limits in CI were clearly higher than those in EI.