Fully automated on-line solid phase extraction coupled to liquid chromatography–tandem mass spectrometry for the simultaneous analysis of alkylphenol polyethoxylates and their carboxylic and phenolic metabolites in wastewater samples

Three different sorbents (i.e. endcapped octadecylsilane, octasilane and styrene-N-vinylpiperidinone co-polymer) were investigated in order to develop an on-line solid phase extraction–liquid chromatographic tandem mass spectrometric method (on-line SPE–LC–MS/MS) for the simultaneous analysis of alkylphenols polyethoxylate (AP EOs, n = 1–8) and corresponding monocarboxylate (AP₁ECs) and phenolic (APs) metabolites. The endcapped octadecylsilane was selected due to its full compatibility with a chromatographic approach, which allowed the elution of positively and negatively ionisable compounds in two distinct retention time windows, using a water–acetonitrile–tetrahydrofuran ternary gradient and a pellicular pentafluorophenyl column. On this SPE sorbent, the composition of the loading/clean-up solution was then optimized in order to achieve the best recoveries of target analytes. Under the best experimental conditions, the total analysis time per sample was 25 min and method detection limits (MDLs) were in the sub-nanograms per litre to nanograms per litre range (0.0081–1.0 ng L⁻¹) for APₙEOs with n = 2–8, AP₁ECs and APs, whereas for AP₁EOs, an MDL of about 50 ng L⁻¹ was found. Using the mass-labelled compound spiking technique, the method performance was tested on inlet and outlet wastewater samples from three activated sludge treatment plants managing domestic and industrial sewages of the urban areas and the textile district of Prato and Bisenzio valley (Tuscany, Italy); in most cases, apparent recovery percentages approximately in the ranges of 50–110 % and 80–120 % were found for inlet and outlet samples, respectively. The on-line SPE–LC–MS/MS analysis of wastewater samples highlighted the presence of target analytes at concentrations ranging from few nanograms per litre to thousands nanograms per litre, depending on the compound and matrix analysed. AP₂ECs were also tentatively identified in outlet samples.