Determination of nonionic polyethoxylate surfactants in wastewater and sludge samples of sewage treatment plants by liquid chromatography-mass spectrometry

Abstract
An analytical method is proposed in order to determine the major nonionic surfactants, octylphenolpolyethoxylates (OPEOs), nonylphenolpolyethoxylates (NPEOs) and aliphatic alcoholpolyethoxylates (AEOs), and their metabolites, nonylphenol and octylphenol in wastewater and sludge samples of sewage treatment plants. This method involved a Soxtec extraction step and a solid phase extraction step for the nonionic surfactant extraction from sludge and wastewater samples, respectively. With both methodologies, all recovery values were higher than 70%. Quantitation and identification of individual compound were carried out by liquid chromatography-mass spectrometry (LC/MS) using electrospray (ESP) as ionization mode. Reverse phase LC chromatography allowed the elution of all oligomer constituents of each homolog component into a single peak. Gathering all the oligomers into a single peak increased the peak intensity and provided a way to determine low concentration of APEOs and AEOs in different environmental matrices. Information on the oligomers distribution of APEOs and AEOs could be obtained by the extraction of selected m/z ions from the TIC chromatograms. Positive ESP LC/MS analyses of AEOs and APEOs yielded primary pseudo-molecular ions of the [M + Na]⁺ type for each oligomer. The negative ionization mode allowed the determination of the two metabolites, nonylphenol and octylphenol, characterized by the pseudo molecular [M-H]^- ion. Limits of detection achieved were 0.1 g/L in wastewater sample and 10 ng/g in sludge samples. The developed LC-ESP/MS method was applied to the analysis of wastewater and sludge samples of two sewage treatment plants located in Orléans (France).