A novel derivative UV–Vis spectrophotometric method for determining rhodamine B in food products

Derivative UV–VIS spectrophotometry is a simple yet highly effective technique for determining color compounds in mix- tures without the need for prior separation. In this study, a sensitive and precise method was developed for the detection of Rhodamine B in food using second-derivative UV–VIS spectroscopy. The zero-crossing technique at 559.5 nm enabled accurate analysis of Rhodamine B in chili products without interference from the sample matrix. The method demonstrated limits of detection of 0.83 mg/kg for chili sauce, 0.85 mg/kg for chili powder, and 1.42 mg/kg for chili oil. Recoveries ranged from 97.6 to 102.1%, highlighting the precision and accuracy of the developed method. This approach offers a reliable alternative to the reversed-phase high-performance liquid chromatography technique. Additionally, its environmental impact was evaluated using the Analytical GREEnness Metric and Complementary Green Analytical Procedure index tools, both of which confirmed the method’s green chemistry credentials. The developed method was successfully applied to analyze 60 commercial samples of chili powder, chili sauce, and chili oil collected from local markets and street food vendors in Ho Chi Minh City.