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 ethoxylates (NPEs) has necessitated the need for the development of specific, and yet efficient, analytical methodologies for their detection. Using seventeen commercial NPEs, all having the general formula 4‐(C9H19)‐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 acetonitrile/tetrahydrofuran (3:1) solvent system prior to mixing with the matrix (α‐cyano‐4‐hydroxycinnamic acid, dissolved in acetonitrile/tetrahydrofuran) solution, and the resulting MALDI‐TOF mass spectra produced mostly sodiated molecules [M + Na]+. For the NPEs in which the major components contain three to ten ethoxy units, the sodiated molecules were detected at a minimum analyte concentration of 10 µg/L, whereas those in which the major components contain eight to fifteen ethoxy units were detected at a minimum concentration of 30 µg/L. Those NPEs containing oligomers in excess of twenty ethoxy units were only detectable at much higher concentration. For examples, Surfonic® N‐300, N‐400, N550, N‐700, N‐800, and N‐1000 had detection limits of (µg/L): 1000, 1600, 2000, 2600, 3500 and 4500, respectively. These variations in instrumental detection limits must be considered when analyzing environmental samples for the presence of nonylphenol ethoxylates. Copyright © 1999 John Wiley & Sons, Ltd.