Voltammetric Quantitative Analysis of Indigo in Water and Urine Using Glassy Carbon Electrode

Abstract

Square wave Voltammetric (SWV) studies of indigo in acidic solutions are reported. The results were applied to develop a determination method for indigo on a glassy carbon electrode (GC). The indigo Cyclic Voltammograms were characterized by reversible and quasi-reversible redox reactions when scanned from −300 mV to 1100 mV. The reversible reaction occurred at E_pa1 = −72 ± 3 mV (A) and E_pc1 = −82 ± 4 mV (A¹), while the quasi was observed at E_pa2 = +615 ± 5 mV (B) and E_pc2 = +585 ± 10 mV (B¹). The SWV Indigo voltammogram is concentration, frequency, amplitude, and starting potential dependent. Optimum parameters for the SWV methods were 40 Hz, 25 mV, −200 mV for frequency, amplitude, and starting potential, respectively, in a solution mixture of 1.0 M KCl and 1.0 M HCl. The method has a linear dynamic graph that ranged from 10⁻⁸ to 10⁻⁶ M with calculated detection limits of 10⁻⁹ M and a sensitivity of 65216 µA/mM. The developed method was successfully used to analyze contaminated river water bodies (Thetsane Stream in Lesotho) and doped urine samples. The amount of indigo in the water was an average of 200 ± 10 µg/ml (n = 4), and an average of 95 ± 15% recoveries was achieved in diluted urine (1:500) samples.

Keywords:

• Indigo
• Square wave voltammetry
• Water

Acknowledgments

This paper is part of a Special Issue of Analytical Letters focusing on papers presented at the 10th International Symposium on Kinetics in Analytical Chemistry (KAC-10).

The authors would like to acknowledge the African Network of Scientific and Technological Institution (ANSTI) for funding through its staffs exchange program and the Sensorlab management for the use of their laboratories facilities.