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A sensitive and selective method for the determination of alcohol ethoxylates (AEOs) and alkylphenol ethoxylates (APEOs) using solid-phase extraction (SPE) and LC-MS/MS was developed and applied to the analysis of water samples. All AEO and APEO homologues, a total of 152 analytes, were analyzed within a run time of 11 min, and the MS allowed for the detection of ethoxymers containing 2-20 ethoxy units (eta(EO) = 2-20). The limits of detection (LOD) were as low as 0.1 pg injected, which generally increased as eta(EO) increased (e.g., as high as 300 pg for eta(EO) =20). Additionally, the responses of the various ethoxymers varied by orders of magnitude, with ethoxymers with eta(EO) = 3-5 being the most sensitive and those with eta(EO) > 15 producing the least response in the MS. Absolute extraction recoveries of the analytes ranged from 37% to 69% in ultrapure water (RSD <= 20%), with the recovery depending on the length of the alkyl chain. Abiotic stability studies were performed, and C14-18 ethoxylates showed significant degrees of degradation. Water samples from the Colorado River were then analyzed for AEOs and APEOs, with absolute extraction recoveries ranging from 33% to 45% (RSD <= 12%). The predominant species observed in most samples were the octylphenol (OP) and nonylphenol (NP) ethoxylates, which contained total concentrations that were greater than 100 ng/L APEOs in a couple samples. Other AEO homologues were identified in the river water samples, including C-13, C-16, C-16, and C-18 ethoxylates, but these compounds. were generally present at much lower levels (i.e., <50 ng/L total concentration). Published by Elsevier B.V.