Application of ultrasound assisted-cloud point extraction coupled with spectrophotometry for the selective extraction/pre-concentration of low levels of inorganic Hg (as Hg₂²⁺/Hg²⁺) from liquid matrices

ABSTRACT

This study presents the analytical characterisation of a low-cost, selective and sensitive method for inorganic Hg (as Hg₂²⁺/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 Hg₂²⁺, 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.

KEYWORDS:

• Inorganic Hg
• ultrasound assisted-cloud point extraction
• Poly(styrene-co-maleic anhydrite)
• 2-aminobenzimidazole
• CTAB
• liquid matrices
• micro-volume UV-vis spectrophotometry

Acknowledgments

The grant supplied by the Scientific Research Projects Commission, Sivas Cumhuriyet University (with project number of F-604) is gratefully acknowledged by authors, directly contributed to the present study. Also, H.B. Zengin likes to thank Prof. Dr. R. Gürkan for providing his analytical laboratory facilities to carry out this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03067319.2022.2161378

Additional information

Funding

This work was supported by Sivas Cumhuriyet University [F-604].