Quenchers in advanced oxidation technologies for analysis of micropollutants by liquid chromatography coupled to mass spectrometry: Sodium sulphite or catalase?

Ana M Gorito; Marta O Barbosa; C Marisa R Almeida; M Fernando R Pereira; Adrián M T Silva; Ana R L Ribeiro

doi:10.1016/j.scitotenv.2019.07.278

Quenchers in advanced oxidation technologies for analysis of micropollutants by liquid chromatography coupled to mass spectrometry: Sodium sulphite or catalase?

Sci Total Environ. 2019 Nov 20:692:995-1004. doi: 10.1016/j.scitotenv.2019.07.278. Epub 2019 Jul 18.

Authors

Ana M Gorito¹, Marta O Barbosa¹, C Marisa R Almeida², M Fernando R Pereira¹, Adrián M T Silva¹, Ana R L Ribeiro³

Affiliations

¹ Laboratory of Separation and Reaction Engineering, Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal.
² Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), Universidade do Porto, Terminal de Cruzeiros do Porto de Leixões, Av. General Norton de Matos s/n, 4450-208 Matosinhos, Portugal.
³ Laboratory of Separation and Reaction Engineering, Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: ritalado@fe.up.pt.

PMID: 31540003
DOI: 10.1016/j.scitotenv.2019.07.278

Abstract

This work aimed to investigate the possible effect of 2 quenchers commonly used in H₂O₂-based advanced oxidation technologies (AOTs), i.e. catalase and sodium sulphite (Na₂SO₃), on the analytical signal of 3 detectors coupled to liquid chromatography (LC): tandem mass spectrometry (LC-MS/MS), fluorescence detection (LC-FD) and LC-diode array detection (LC-DAD). The observation of analytical interferences for a group of compounds when studying the removal by continuous mode UV/H₂O₂ of 26 micropollutants (MPs) from a spiked surface water (SW), for which the residual H₂O₂ in the samples was quenched by Na₂SO₃, triggered the need of understanding these effects and thus catalase was used as comparative quencher. From the 26 MPs having a wide range of polarity and pK_a, those monitored after electrospray ionization (ESI) under positive ionization (PI) mode and presenting a pK_a higher than 5.9 revealed a great signal suppression, but only when using Na₂SO₃ as H₂O₂ quencher. In this sense, we further explored this effect by selecting 2 MPs, metoprolol and diclofenac, which had respectively signal suppression and no interference in the LC-MS/MS response. These MPs were analysed before and after addition of H₂O₂ and catalase or Na₂SO₃ in reaction vials, using: (i) different detectors coupled to LC, namely LC-MS/MS with ESI under PI and negative ionization (NI) modes, LC-FD and LC-DAD; (ii) different environmental matrices (SW, drinking water, wastewater) and ultrapure water; and (iii) different magnitude levels (0.1-10 mg L^-1). The results demonstrated a remarkable signal suppression in LC-MS/MS analyses under PI mode for those compounds with pK_a higher than 5.9, confirming the interfering effect of H₂O₂/Na₂SO₃. To the best of our knowledge, the analytical interference in the LC-MS/MS analysis, after adding Na₂SO₃ to quench H₂O₂ in AOTs experiments was never reported before and the results presented herein support the recommendation to use catalase instead of Na₂SO₃ as quencher in AOTs studies.

Keywords: Advanced oxidation processes; Fenton; Hydrogen peroxide; Matrix effects; Ozonation; Sodium sulphite.