Determination of inorganic mercury using a polyaniline and polyaniline-methylene blue coated screen-printed carbon electrode

Abstract

Inorganic mercury ions (Hg²⁺) in laboratory prepared solutions were determined with a screen-printed carbon electrode (SPCE) coated with a polyaniline-methylene blue (PANI-MB) polymer layer. The structure and properties of the PANI-MB polymer layer were compared to that of normal polyaniline (PANI) in order to elucidate the structure of the PANI-MB layer. The electrically-conducting polymers were prepared by electrochemical polymerisation of monomer solutions of aniline, and mixed solutions of aniline with methylene blue onto respective screen-printed carbon electrodes (SPCEs). Scanning Electron Microscopy (SEM) analyses of the SPCE polymer coated electrodes have shown that nanostructured materials have formed with the diameters of the PANI nanoclusters and PANI-MB nanorods at approximately 200 nm. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of 1 × 10⁻⁶ M Hg²⁺, in the presence of the SPCE/PANI-MB polymer sensor electrode. The Hg²⁺ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg²⁺ determination included the supporting electrolyte concentration and the accumulation time. The results obtained have shown that the SPCE/PANI-MB polymer sensor electrode operates optimally at a pH 2, with the supporting electrolyte concentration at 0.5 M HCl. A linear calibration curve was found to be in the range of 1 × 10⁻⁸ M to 1 × 10⁻⁵ M Hg²⁺ after 120 s of pre-concentration. The detection limit was calculated and found to be 54.27 ± 3.28 µg L⁻¹ of Hg²⁺. The results have also shown that a conducting polymer modified SPCE sensor electrode can be used as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg²⁺ ions.

Keywords:

• inorganic mercury determination
• polyaniline nanoclusters
• polyaniline-methylene blue nanorods
• screen-printed carbon electrode (SPCE)
• differential pulse anodic stripping voltammetry (DPASV)

Acknowledgements

This research was supported by funding received from the CSIR's parliamentary grant (PG) process and the National Research Foundation (NRF) of South Africa in aide of the South African Mercury Assessment Programme's (SAMA) research activities into the quantification of Hg levels in South African water resources. The collaboration with the research laboratories of the Universities of the Western Cape (RSA), Dublin City University (DCU) and Connecticut (USA) is also acknowledged.