Molecular distribution of some commercial nonylphenol ethoxylates using matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Nonylphenol ethoxylates (NPEs) belong tea a group of nonionic surfactants t hat are collectively referred to as alkylphenol ethoxylates (APEs), APEs fi nd widespread use in heavy-duty commercial and household cleaning formulati ons, shampoos, and industrial processing, i.e. textile manufacture. Their e nvironmental impact depends on the molecular distribution and the extent of their biodegradation in municipal sewage systems, waterways and rivers. We have established two sample preparation methods that have enabled the dete rmination of the molecular distributions of six commercial nonylphenol etho xylates using matrix-assisted laser desorption/ionization (MALDI) time-of-f light (TOF) mass spectrometry (MS), In both methods, alpha-cyano-4-hydroxyc innamic acid, dissolved in acetonitrile/tetrahydrofuran, was used as the ma trix. In one set of experiments, the NPEs were dissolved in an acetonitrile /tetrahydrofuran solvent system prior to mixing with the matrix solution, a nd the resulting MALDI-TOF mass spectra produced mostly sodiated molecules [M + Na](+). The NPEs, all having the formula 4-(C9H19)-C6H4-(OCH2CH2)(n)-O H, are Surfonic (R)N-95, N-100, N-102, N-120, N-150 and N-300, Surfonic N-9 5 and N-100 gave n values of 5-20; Surfonic N-102, N-120, N-150, and N-300 gave n values of 5-21, 5-22, 8-25 and 15-40, respectively. In order to deve lop a sample preparation method that could be used with less polar NPEs, we dissolved the NPEs (except N-300) in pentane prior to mixing with the matr ix solution, and found that the MALDI spectral quality was unaffected by th e solvent systems. Copyright (C) 1999 John Wiley & Sons, Ltd.