Different Approaches for Paraquat Quantification in Waters

Abstract

Three analytical methodologies for paraquat (PQ) identification and quantification in waters were developed and validated in response to different scenarios: a direct injection-liquid chromatography–diode array detector (DI-LC–DAD) method for emergency situations, as occurs when there is a suspicion of contamination of drinking water networks; a solid phase extraction-liquid chromatography-diode array detector (SPE-LC–DAD) method to control the drinking water quality and a direct injection-liquid chromatography-mass spectrometry (DI-LC–MS) method for confirmation purposes and identification of PQ degradation by-products. Limits of detection of 10 µg/L, 0.04 µg/L, and 20 µg/L PQ were reached for DI-LC–DAD, SPE-LC–DAD, and DI-LC–MS methods, respectively. The PQ analytical response of DI-LC–DAD method was tested in different types of water and in the presence of other species (Fe(II), H2O2 and Na2SO3) or compounds resulting from the contact of the water with deposits and Pseudomonas fluorescens cells that exist in drinking water networks. Additionally, the method response was assessed when Gramoxone was used as PQ source instead of the analytical standard. Global uncertainties below 6%, 11%, and 13% were found for DI-LC–MS, SPE-LC–DAD, and DI-LC–DAD, respectively, for the most part of the calibration ranges. All methods proved to be precise, accurate, and suitable for the purpose that they were designed.