Emulsification liquid-liquid microextraction coupled with droplet digital image colorimetric detection for determination of rhodamine B in food and beverage samples

An analytical method combining fatty acid-emulsification liquid-liquid microextraction (FA-ELLME) with solidification of floating drops (SFD) and droplet digital image colorimetry (DDIC) was developed for the analysis of rhodamine B (RhB) in food and beverage samples. This work applied an emulsified amphiphilic fatty acid as an extracting solvent and a freezing procedure for extracting phase separation. A 7 mL sample volume adjusted to pH 5 was extracted with a drop of 35 μL of octanoic acid (0.5%v/v). The emulsification was initiated by shaking for 10 s followed by centrifugation for 5 min. The floating drops containing RhB were solidified in an ice bath, separated from the solution, defrosted, and dropped on the paper platform for DDIC analysis. The limit of detection (LOD) and limit of quantification (LOQ) were 1.8 μg L⁻¹ and 6.0 μg L⁻¹, respectively. The linear range was 10 - 40 μg L⁻¹ (R² = 0.997). The method was applied to determine RhB in beverage, candy, jelly, and chili sauce samples. The relative recovery percentages (RR%) between 73% and 113% were achieved.