Emulsification microextraction using surfactant coupled with colorimetric detection for determination of synthetic dyes in food

Abstract

In this thesis, solidification of floating organic drop-emulsification liquid-liquid microextraction (SFOD-ELLME) was combined with digital image colorimetry (DIC) for the analysis of synthetic dyes, such as rhodamine B (RhB) and crystal violet (CV) in food and drink samples. Here, the extraction was performed by using emulsified fatty acid surfactant and freezing procedure to separate the extracting phase. The solidified floating organic drop was then taken out, liquified and dropped on the paper platform for digital image colorimetric analysis. The response surface methodology-central composite design (RSM-CCD) was used to optimize some variables that influence the extraction efficiency. A sample of 7 mL was used and adjusted to pH 7 and 8 for CV and RhB, respectively prior to extraction. The extraction phase was 21.6 μL octanoic acid. The extraction phase was emulsified by manually shaking for 10 s and centrifugation at 3000 rpm for 5 min. The digital image was taken by the smartphone camera in the light-controlled box. The distance between camera and the paper platform was kept at 36 cm. The color was analyzed by ImageJ program using red channel. Limit of detection (LOD) and limit of quantification (LOQ) for CV were 0.8 μg/L and 3 μg/L; 3 μg/L and 10 μg/L for RhB. The linear ranges were 3-20 μg/L (R2 = 0.999) for CV and 10-40 μg/L (R2 = 0.995) for RhB. The method was applied to determine RhB in beverage, candy, jelly, and chili sauce samples and CV in drinking water samples. The relative recovery percentages (RR%) between 73 % and 113 % were achieved.