Green and cost-effective voltammetric assay for spiramycin based on activated glassy carbon electrode and its applications to urine and milk samples

Abstract

A simple, cost-effective, and efficient differential pulse voltammetric (DPV) assay for monitoring spiramycin adipate (SPA) in its dosage forms, urine, and milk samples at an activated glassy carbon electrode (GCE) was developed. GCE was electrochemically activated by anodization at a high positive voltage (2.5 V). The activated glassy carbon electrode (AGCE) was surface characterized, optimized, and utilized for the electrochemical assay of SPA. The electrochemical behavior of the AGCEs was investigated using cyclic voltammetry (CV) which shows a remarkable increase in the anodic peak of SPA in comparison with GCE. This behavior reflects a remarkable increase in the electrocatalytic oxidation of SPA at AGCE. The impacts of various parameters such as scan rate, accumulation time, and pH were investigated. The analytical performance of the activated glassy carbon electrodes was studied utilizing DPV. Under optimum conditions, the oxidation peak current exhibited two linear ranges of 80 nm to 0.8 μM and 0.85-300 μM with a lower limit of detection (LOD) of 20 nM. The developed assay exhibited high sensitivity, excellent repeatability, and good selectivity. Additionally, the developed SPA-sensitive modified GCE was successfully applied for SPA assay in its pharmaceutical dosage form and diluted biological fluids as well, with satisfactory recovery results which correlated well with the results obtained using spectrophotometry.

Fig. 1. Repetitive cyclic voltammograms of GCE in 0.1 M phosphate buffer (pH 7.0). Scan rate: 100 mV s⁻¹.

Fig. 2. CVs of 1.0 × 10⁻³ M SPA in 0.1 M phosphate buffer pH 7.0 at bare GCE (a), and AGCE (c). Curve (b) represents the CV of AGCE in a blank solution (0.1 M phosphate buffer-free from SPA). Scan rate: 100 mV s⁻¹.

Scheme 1. A schematic presentation of the possible electrooxidation mechanism of SPA at AGCE.

Fig. 3. (A) Effect of accumulation time on the CV oxidation peak currents of 5.0 × 10⁻⁵ M SPA at AGCE. (B) Effect of solution pH on the CV oxidation peak currents of 5.0 × 10⁻⁵ M SPA at AGCE. (C) CVs of the AGCE at different scan rates in 0.1 M phosphate buffer (pH 7.0) containing 5.0 × 10⁻⁵ M SPA, scan rates (from 1 to 9): 10, 30, 50, 100, 140, 180, 200, 250 and 300 mV s. (D) A plot of peak current (i_p) versus the square root of the scan rate (ν^1/2).

Fig. 4. (A) DPVs at the AGCE in 0.1 M phosphate buffer (pH 7.0) containing different concentrations of SPA, (from 1 to 11): 0.08, 0.8, 5.9, 15.4, 43.0, 64.9, 85.8, 128.6, 172.6, 212.4 and 305.2 μM at scan rate: 100 mV s⁻¹. (B) The corresponding calibration plot for SPA at AGCE.