Green Dispersive Liquid–Liquid Microextraction Using an Octanol-Menthol-Based Deep Eutectic Solvent for Sensitive UV–Vis Determination of Rhodamine B in Food and Water Samples

A new green dispersive liquid–liquid microextraction (DLLME) technique was developed using a deep eutectic solvent (DES) including 1-octanol and menthol (OCT-MEN) for the separation, preconcentration, and UV–Vis spectrophotometric analysis of Rhodamine B (RhB) in food and water samples. The prepared DES was characterized by using FTIR and NMR techniques. The procedure was optimized under the following parameters: pH 2, OCT-MEN volume of 300 µL (1.5:1 molar ratio), ultrasonication for 1 min, and centrifugation for 2 min. The approach exhibited acceptable analytical performance, characterized by a low limit of detection (LOD) of 5.1 µg L⁻ 1 , a limit of quantification (LOQ) of 17.0 µg L⁻ 1 , and good linearity (R 2 = 0.999). The application to actual samples, such as juices, soft drinks, teas, tap water, cave water, and wastewater, resulted in recovery rates ranging from 90 to 117%, with relative standard deviations not exceeding 8.9%. Statistical analysis using t-tests and one-way ANOVA demonstrated no significant changes when compared to HPLC-FLD data. The evaluation of greenness using White Analytical Chemistry and ComplexMoGAPI tools verified its significant environmental friendliness. The DLLME-based OCT-MEN method provides a simple, accurate, sustainable, and economical technique for the quantification of RhB in food and water samples.