Evaluation of ozone-based treatment processes for wastewater containing microcontaminants using LC-QTRAP-MS and LC-TOF/MS

Abstract

This article describes the development of an enhanced liquid chromatography-mass spectrometry (LC-MS) method for the analysis of a selected group of 57 organic contaminants in wastewater. This group comprises 39 pharmaceuticals belonging to different therapeutical classes and 10 of their most frequent metabolites. Six pesticides and two disinfectants were also included. The LC-MS method was developed using a hybrid quadrupole/linear ion trap (Q TRAP) analyzer operating in selected reaction monitoring (SRM) mode (in both positive and negative electrospray ionization) in combination with a time-of flight (TOF) mass analyser. The application of both techniques provided very good results in terms of accurate quantification and unequivocal identification. Quantification was based on the use of a linearly accelerating (LINAC) high-pressure collision cell, which enable the analysis of a high number of compounds with enough acquisition data points for an optimal peak definition in SRM. Unequivocal identification was provided by the acquisition of at least two SRM transitions and by obtaining accurate mass measurements of the identified compounds with errors lower than 2 ppm. As an alternative for compounds where a second transition cannot be detected by Q-Trap-MS, the application of survey scans in enhanced product ion (EPI) was evaluated. The analytical performance of the method was evaluated in effluent wastewater samples. Linearity of response over three orders of magnitude was demonstrated (R2>0.99 for most compounds). Matrix effects resulting in suppression of the response were frequently observed, between 2-50% for most of compounds, except 4-DAA and 4-AA, which exhibit higher values (68%). Signal enhancement was also detected in 16 compounds. Method limits of detection (LOD) were between 0.1-50 ng L(-1). Finally, the methodology was successfully applied to the evaluation of the efficiency of two ozone-based treatments applied to the effluent from the secondary clarifier of a municipal wastewater treatment facility. Preliminary results are presented demonstrating that ozonation of wastewaters degrade pharmaceuticals with a high efficiency. Removals higher than 90% were reached for most of target analytes.