Liquid chromatography quadrupole time-of-flight mass spectrometry quantification and screening of organophosphate compounds in sludge

For the first time, we assess the performance of liquid chromatography (LC) quadrupole time-of-flight (QTOF) mass spectrometry (MS) for the selective quantification of eight organophosphate compounds (OPs), used as plasticizers and flame retardants additives, in sludge from urban sewage treatment plants (STPs). Moreover, the usefulness of accurate, full scan MS and MS/MS spectra to screen and to confirm the presence of additional OPs, without using reference standards, in sludge samples is discussed. Matrix solid-phase dispersion (MSPD) was used as a sample preparation technique. Under optimized conditions, MSPD provided quantitative recoveries for the group of targeted analytes, requiring just 15 mL of solvent and integrating extraction and clean-up processes in the same step. For these species, the achieved limits of quantification (LOQs) varied between 2 and 50 ng g−1 and the efficiency of electrospray ionization (ESI) did not change significantly between pure standards and sludge extracts. Among targeted OPs, tri(chloroisopropyl) phosphate (TCPP), tributoxyethyl phosphate (TBEP) and triphenyl phosphate (TPP) were ubiquitous in sludge. The average concentrations of TCPP and TBEP stayed above 700 ng g−1, whereas the mean value for TPP was 67 ng g−1. Full scan, accurate spectra provided relevant clues for the screening of additional OPs, using a database containing just their empirical formulae and exact molecular weights; however, the occurrence of in-source fragmentation processes hampered the detection and correct identification of those species which did not render the expected [M+H]+ molecular ion, as was the case of 2-ethylhexyl-diphenyl phosphate (EHDPP).