Use of selective quenching of a photoluminescent probe based on a Eu(III) β-diketonate complex for determination of methylmercury in produced water after liquid-liquid extraction

Abstract

An Eu(III) β-diketonate complex was produced and employed as a photoluminescent probe to determine methylmercury (CH₃Hg⁺). To establish its molecular structure, the Eu(III) complex was characterized by elemental (CHNS) and thermogravimetric analyses and infrared spectroscopy. After establishing robust conditions to use the Eu(III) complex as an analytical probe, it was employed for the analysis of produced water (PW) samples with the analytical response based on the luminescence suppression proportional to the concentration of CH₃Hg⁺ (a linear model after normalization of the response within the concentration range from 0.2 μg L^-1 up to 2.0 μg L^-1). Selectivity was guaranteed by a simple liquid-liquid extraction of the analyte in dichloromethane, which also allowed a 50 times pre-concentration factor. The instrumental limit of quantification of 0.2 μg L^-1 is equal to the limit established in Brazilian resolution for total mercury content in waters, but pre-concentration (50 times factor) improved the overall method limit of quantification down to 4 ng L^-1. Recovery results agreed with the ones achieved using cold vapor atomic absorption spectrometry.

Keywords: Eu(III) β-diketonate complex; Fluorescent probe; Methylmercury; Produced water.