Determination of the instrumental detection limits of commercial nonylphenol ethoxylates with a wide range of molecular masses using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Recent interest in the environmental fate and impact of nonylphenol ethoxyl ates (NPEs) has necessitated the need for the development of specific, and yet efficient, analytical methodologies for their detection. Using seventee n commercial NPEs, all having the general formula 4-(C9N19)-C6H4-(OCH2CH2)( n)-OH, we have established minimum concentrations at which matrix-assisted laser desorption ionization (MALDI)/time-of-flight (TOF)/mass spectrometry (MS) can be used in their detection. The NPEs were dissolved in an acetonit rile/tetrahydrofuran (3:1) solvent system prior to mixing with the matrix ( alpha-cyano-4-hydroxycinnamic acid, dissolved in acetonitrile/tetrahydrofur an) solution, and the resulting MALDI-TOF mass spectra produced mostly sodi ated molecules [M + Na](+). For the NPEs in which the major components contain three to ten ethoxy unit s, the sodiated molecules were detected at a minimum analyte concentration of 10 mu g/L, whereas those in which the major components contain eight to fifteen ethoxy units were detected at a minimum concentration of 30 mu g/L. Those NPEs containing oligomers in excess of twenty ethoxy units were only detectable at much higher concentration. For examples, Surfonic(R) N-300, N-400, N550, N-700, N-800, and N-1000 had detection limits of (mu g/L): 100 0, 1600, 2000, 2600, 3500 and 4500, respectively. These variations In instr umental detection limits must be considered when analyzing environmental sa mples for the presence of nonylphenol ethoxylates. Copyright (C) 1999 John Wiley & Sons, Ltd.