Activated Glassy Carbon Electrode as an Electrochemical Sensing Platform for the Determination of 4-Nitrophenol and Dopamine in Real Samples

Abstract

Glassy carbon electrode (GCE) was electrochemically activated using a repetitive cyclic voltammetric technique to develop an activated glassy carbon electrode (AGCE). The developed AGCE was optimized and utilized for the electrochemical assay of 4-nitrophenol (4-NP) and dopamine (DA). Cyclic voltammetry (CV) was employed to investigate the electrochemical behavior of the AGCE. Compared to the bare GCE, the developed AGCE exhibits a significant increase in redox peak currents of 4-NP and DA, which indicates that the AGCE significantly improves the electrocatalytic reduction of 4-NP and oxidation of DA. The electrochemical signature of the activation process could be directly associated with the formation of oxygen-containing surface functional groups (OxSFGs), which are the main reason for the improved electron transfer ability and the enhancement of the electrocatalytic activity of the AGCE. The effects of various parameters on the voltammetric responses of the AGCE toward 4-NP and DA were studied and optimized, including the pH, scan rate, and accumulation time. Differential pulse voltammetry (DPV) was also utilized to investigate the analytical performance of the AGCE sensing platform. The optimized AGCE exhibited linear responses over the concentration ranges of 0.04-65 μM and 65-370 μM toward 4-NP with a lower limit of detection (LOD) of 0.02 μM (S/N = 3). Additionally, the AGCE exhibited a linear responses over the concentration ranges of 0.02-1.0 and 1.0-100 μM toward DA with a lower limit of detection (LOD) of 0.01 μM (S/N = 3). Moreover, the developed AGCE-based 4-NP and DA sensors are distinguished by their high sensitivity, excellent selectivity, and repeatability. The developed sensors were successfully applied for the determination of 4-NP and DA in real samples with satisfactory recovery results.

Scheme 1. Proposed Mechanism of Possible Redox Processes Occuring at the Surface of the AGCE

Figure 1

CVs of the bare GCE (a) and AGCE (b) in 0.1 M PBS (pH 7.0) containing 1 × 10^–4 M 4-NP (A) and 5 × 10^–4 M DA (B) at a scan rate of 100 mVs^–1. Curve (c) represents the CV of the AGCE in a blank solution (0.1 M PBS free from 4-NP and DA).

Figure 2

(A) CVs of 0.1 M PBS (pH 7.0) containing 1 × 10^–4 M 4-NP at the AGCE as measured at different accumulation times (from 20 to 180s). (B) Effect of accumulation time on the cathodic peak currents of 4-NP. (C) CVs of 0.1 M PBS (pH 7.0) containing 5 × 10^–4 M DA at the AGCE as measured at different accumulation times (from 0 to 90 s). (D) Effect of accumulation time on the anodic peak currents of DA.

Figure 3

(A) CVs of 1 × 10^–4 M 4-NP at the AGCE as measured at different pH values. (B) Relationship between pH and the cathodic peak currents of 4-NP. (C) CVs of 5 × 10^–4 M DA at the AGCE as measured at different pH values. (D) Relationship between pH and the formal potential (E⁰′) (a) and the relationship between pH and the anodic peak currents of DA (b).

Scheme 2. Reduction Mechanism of 4-NP at the AGCE

Scheme 3. Oxidation Mechanism of DA at the AGCE

Figure 4

(A) CVs of the AGCE at different scan rates in 0.1 M PBS (pH 7.0) containing 1 × 10^–4 M 4-NP (A) and 5 × 10^–4 M DA (C). Scan rates from 10 to 300 mVs^–1. (B) Plot of the cathodic peak current (i_p) of 4-NP versus the square root of the scan rate (ν^1/2). (D) Plots of the anodic peak current (i_pa) and cathodic peak current (i_pc) of DA versus the square root of the scan rate (ν^1/2).

Figure 5

(A) DPVs of different concentrations of 4-NP as measured in 0.1 M PBS, pH 7.0, at the AGCE. Concentrations (from 1 to 15): 0.04, 0.08, 0.52, 1.0, 3.5, 5.8, 8.3, 10.7, 20.2, 43.0, 65.0, 128.74, 212.3, 290.0, and 370.0 μM. (B) Corresponding calibration plot for 4-NP at the AGCE. (C) DPVs of different concentrations of DA as measured in 0.1 M PBS, pH 7.0, at the AGCE. Concentrations (from 1 to 13): 0, 0.02, 0.04, 0.06, 0.08, 0.5, 0.8, 1.0, 20.0, 40.0, 55.0, 79.0, and 100.0 μM. (D) Corresponding calibration plot for DA at the AGCE. The inset of (D) indicates the responses at low concentrations of DA.