Highly sensitive voltammetric determination of the fungicide fenhexamid using a cost-effective and disposable pencil graphite electrode

Abstract

A differential pulse voltammetric (DPV) method is proposed for the highly sensitive determination of fenhexamid (FHX) based on both electrooxidation and electroreduction processes using a disposable and cost-effective pencil graphite electrode (PGE). The electrochemical oxidation and reduction mechanisms of FHX at the PGE were elucidated by recording cyclic voltammograms at various pH values of Britton-Robinson buffer (BRB) solutions at a scan rate of 50 mV s^-1 and different scan rate values in the range 10-400 mV s^-1 at selected pH of BRB (pH 2.0). Differential pulse voltammograms recorded under optimized conditions revealed an oxidation peak of FHX around + 0.65 V and a reduction peak of FHX around + 0.45 V. The DPV analysis of FHX revealed two linear ranges: 0.001-0.01 µmol L^-1 and 0.01-5.0 µmol L^-1 for the anodic peak, and 0.001-0.1 µmol L^-1 and 0.1-5.0 µmol L^-1 for the cathodic peak. The limits of detection were 0.34 nmol L^-1 and 0.32 nmol L^-1 for the anodic and cathodic peaks, respectively. The proposed methodology demonstrated satisfactory selectivity, as selected pesticides, certain electroactive compounds, and cationic species tested did not interfere with the voltammetric determination of FHX, particularly during its reduction. The recovery results, showing values close to 100% obtained from the analysis of real samples spiked with FHX, indicated that this methodology can accurately determine FHX in water and soil samples.

Keywords: Differential pulse voltammetry; Electroanalysis; Electrochemical sensor; Graphite electrode; Pesticide detection.

Fig. 1

Cyclic voltammograms of (A) 5.0 mmol L⁻¹ redox marker containing 0.1 mol L⁻¹ KCl and (B) 27.5 µmol L⁻¹ FHX in pH 2.0 of BRB solution containing 0.1 mol L⁻¹ KCl solution recorded on the (a) PGE, (b) CPE, (c) SPCE, and (d) GCE at a scan rate of 50 mV s⁻¹

Fig. 2

A Cyclic voltammograms of 27.5 µmol L⁻¹ FHX recorded at the PGE in 0.1 mol L⁻¹ H₂SO₄ and BRB solutions containing 0.1 mol L⁻¹ KCl solution prepared at varying pH values between 2.0 and 10.0 at a scan rate of 50 mV s⁻¹. B The linear dependences of (a) oxidation and (b) reduction peak potentials vs. pH

Scheme 1

Proposed mechanism of electrochemical behavior of FHX exhibiting a quasi-reversible redox couple at the PGE

Fig. 3

Cyclic voltammograms of 27.5 µmol L⁻¹ FHX recorded at the PGE in a pH 2.0 of BRB solution containing 0.1 mol L⁻¹ KCl solution at varying scan rates ranging from 10 to 400 mV s⁻¹

Fig. 4

A DPVs of FHX showing concentration-dependent (from 0.001 to 10 µmol L⁻¹) responses scanned towards the anodic region using the PGE in pH 2.0 of BRB solution containing 0.1 mol L⁻¹ KCl solution. The magnified version of DPVs for the range between 0.001 and 0.1 µmol L⁻¹ is provided on the right side. Linear calibration curves in the range (B) from 0.001 to 0.01 µmol L⁻¹ and (C) from 0.01 to 5.0 µmol L⁻¹

Fig. 5

A DPVs of FHX showing concentration-dependent (from 0.001 to 10 µmol L⁻¹) responses scanned towards the cathodic region using the PGE in pH 2.0 of BRB solution containing 0.10 M KCl solution. The magnified version of DPVs for the range between 0.001 and 0.1 µmol L⁻¹ is given on the right side. Linear calibration curves in the range from (B) 0.001 to 0.1 µmol L⁻¹ and (C) from 0.1 to 5.0 µmol L⁻¹