Sustainable and modification-free voltammetric quantification of thymoquinone in Nigella sativa oil-based food products.

Thymoquinone, a bioactive compound with antioxidant and anti-inflammatory properties, is a major component of Nigella sativa (black cumin) oil, widely used in functional foods and dietary supplements. In this study, we developed a rapid, eco-friendly, and cost-effective voltammetric method for the direct determination of the target analyte in real oil-based food matrices using an unmodified boron-doped diamond electrode. The method requires no chemical pretreatment or extraction and uses only ethanol and water as solvents. Key parameters, including electrolyte pH and square wave voltammetry settings, were optimized for analytical sensitivity. Under optimal conditions, the method showed a linear response from 0.070 to 70.0 μmol·L-1, with LOD of 7.5 nmol·L-1(1.2 ng·mL-1). The method was successfully applied to commercial oil and supplement samples, yielding results in agreement with manufacturer claims. Its simplicity and sustainability make it suitable for routine quality control in food and nutraceutical analysis without the need for chemical extraction or sensor modification.