Glassy carbon electrode modified with rice husk biochar for sodium diclofenac determination using square-wave voltammetry

Diclofenac, an anti-inflammatory drug, is an environmental concern due to its high consumption and hazardous effects on the environment. To address this issue, developing new diclofenac sensors is essential. Therefore, this study investigated a voltammetric method using biochar-modified electrodes for diclofenac detection. Among the biochars produced under different pyrolysis conditions, the one obtained at 700 °C for 120 min exhibited the most favorable characteristics for electrochemical applications, including higher thermal stability, increased carbonization, and an enhanced surface area. The application of this biochar to modify a glassy carbon electrode (GCE) resulted in a 73% increase in peak current using square-wave voltammetry compared to the bare GCE. This enhancement is attributed to improved interactions between the drug and the biochar produced under severe pyrolysis conditions, such as non-covalent π–π interactions and hydrophobic effects. Under optimized conditions, the developed sensor demonstrated a linear response from 0.25 to 1.25 mg L⁻¹, described by the linear regression equation: <i>I_p</i> = 1.30 × 10⁻⁷x -4.44 × 10⁻⁹, with a correlation coefficient of 0.9905. The limits of detection and quantification for sodium diclofenac measurement were 0.0364 and 0.1103 mg L⁻¹, respectively. The recovery analysis of sodium diclofenac commercial tablets achieved 112.05 ± 5.75% when compared to the concentration reported on the product label.