Application of ultrasound assisted-cloud point extraction coupled with spectrophotometry for the selective extraction/pre-concentration of low levels of inorganic Hg (as Hg2 2+/Hg2+) from liquid matrices

Abstract

ABSTRACT This study presents the analytical characterisation of a low-cost, selective and sensitive method for inorganic Hg (as Hg2 2+/Hg2+) determination in liquid matrices based on spectrophotometry. The novelty of the study lies in combining the pre-concentration of i-Hg with spectrophotometry after chelation with the 2-aminobenzimidazole modified amidic copolymer to increase the selectivity and sensitivity of the method. The method involves ultrasonic extraction of the samples in a dilute acid mixture of HClO4-HCl-CH3COOH and mixture of Cu(II)-oxalic acid-KCl adjusted to pH 5.0 in parallel, pre-con centration using UA-CPE process on modified amide copolymer, and absorbance measurement at 332 nm using a micro-volume UV-spectrophotometer. The figures of merit were discussed in relation with the demands in the national/international regulations and standards on the determination of toxic i-Hg in water intended for human consumption. After a pre-concentration of 62.5-fold, the limits of detection and quantification (LODs, LOQs) were 0.24 and 0.22 μg L−1 allowing the use of the method for i-Hg determination in liquid matrices such as cold-/hot-spring waters, plain soda, bottled drinking waters, and carbonated soft drinks. For concentrations of Hg2 2+, Hg2+ and total Hg in the range of <LOD, 0.35–4.20, and 0.40–4.50 μg L−1, the precision was 3.3–8.3%, below and little above the maximum limits of 1.0 µg L−1 set in the mentioned legislation. The recovery of 92–96.4% and the precision in the range of 4.1–5.4% in the analysis of two certified waters were found to be satisfactory, so as to validate the method. The method developed is cost-effective and enables us to achieve i-Hg determination in liquid matrices complying with European legislation. The system has a good potential for the future and analytical perspectives.