Design and Characterization of Electrochemical Sensor for the Determination of Mercury(II) Ion in Real Samples Based upon a New Schiff Base Derivative as an Ionophore

Abstract

The present paper provides a description of the design, characterization, and use of a Hg²⁺ selective electrode (Hg²⁺-SE) for the determination of Hg²⁺ at ultra-traces levels in a variety of real samples. The ionophore in the proposed electrode is a new Schiff base, namely 4-bromo-2-[(4-methoxyphenylimino)methyl]phenol (BMPMP). All factors affecting electrode response including polymeric membrane composition, concentration of internal solution, pH sample solution, and response time were optimized. The optimum response of our electrode was obtained with the following polymeric membrane composition (% w/w): PVC, 32; o-NPOE, 64.5; BMPMP, 2 and NaTPB, 1.5. The potentiometric response of Hg²⁺-SE towards Hg²⁺ ion was linear in the wide range of concentrations (9.33 × 10^-8-3.98 × 10^-3 molL^-1), while, the limit of detection of the proposed electrode was 3.98 × 10^-8 molL^-1 (8.00 μg L^-1). The Hg²⁺-SE responds quickly to Hg²⁺ ions as the response time of less than 10 s. On the other hand, the slope value obtained for the developed electrode was 29.74 ± 0.1 mV/decade in the pH range of 2.0-9.0 in good agreement with the Nernstian response (29.50 mV/decade). The Hg²⁺-SE has relatively less interference with other metal ions. The Hg²⁺-SE was used as an indicator electrode in potentiometric titrations to estimate Hg²⁺ ions in waters, compact fluorescent lamp, and dental amalgam alloy and the accuracy of the developed electrode was compared with ICP-OES measurement values. Moreover, the new Schiff base (BMPMP) was synthesized and characterized using ATR-FTIR, elemental analysis, ¹H NMR, and ¹³C NMR. The PVC membranes containing BMPMP as an ionophore unloaded and loaded with Hg(II) are reported by scanning electron microscope images (SEM) along with energy-dispersive X-ray spectroscopy (EDX) spectra.

Keywords: ISE-Hg; PVC membrane; Schiff base; ionophore; mercury selective electrode.

Scheme 1

Synthetic protocol of (4-bromo-2-[(4-methoxyphenylimino)methyl]phenol, BMPMP.

Figure 1

The influence of membrane composition on the potential response of the Hg²⁺-ISEs.

Figure 2

Calibration curve of the Hg²⁺-SE (ISE7) based on the BMPMP as ionophore.

Figure 3

ATR–FTIR spectra of Hg²⁺–SE membrane: (A) membrane before being superimposed in Hg²⁺–SE and (B) the membrane after using for sensing Hg²⁺ ions.

Figure 4

SEM micrographs of (A) control membrane and (B) optimized membrane used for sensing mercury (II).

Figure 5

EDX spectra of (A) control membrane and (B) membrane selected for sensing mercury (II).

Figure 5

EDX spectra of (A) control membrane and (B) membrane selected for sensing mercury (II).

Figure 6

The relation between −log [Hg²⁺] and the potential of Hg²⁺–SE at different concentrations of internal solution.

Figure 7

Role of test solution’s pH on the potential response of Hg²⁺–SE at different concentrations: (blue) 1.0 × 10^–2 and (red) 1.0 × 10^–3 molL^–1.

Figure 8

The relation of response time with Hg²⁺–SE potential at different concentrations of analyte and 298K: The curves of a, b, c, d, e, and f shows this relation at the Hg²⁺ concentrations of 1.06 × 10^–7, 1.06 × 10^–6, 1.06 × 10^–5, 1.0 × 10^–4, 1.0 × 10^–3 and 1.0 × 10^–2 molL^–1, respectively.

Figure 9

Life time of the proposed Hg²⁺-SE for a period of 112 days.

Figure 10

The values of $K_{Hg,M}^{pot}$ of proposed Hg²⁺–SE for variety of different cations.

Figure 11

Potentiometric titration curve of standard solution of Hg(NO₃)₂ with EDTA solution using our proposed electrode as an indicator electrode at optimized conditions. The concentrations used are mentioned in the text.