Development of a green method for the microextraction and determination of some trace species in seafood using magnetic deep eutectic solvents

The aim of this thesis is to determine trace amounts of crystal violet (CV) and cadmium (Cd(II)) in water samples and seafood, and to develop a magnetic deep eutectic solvent-based dispersive liquid-liquid microextraction (MDES-DLLME) method for their pre-concentration before determination. After the microextraction process, UV-Vis spectrophotometry was used for the determination of CV, and flame atomic absorption spectrometry was used for the determination of Cd(II). In this developed method, the extraction solvent was a deep eutectic solvent (DES), which is easy to synthesize, low in toxicity, stable, inexpensive, and classified as a green solvent. Thanks to the magnetic feature, phase separation is easily achieved by applying an external magnetic field, without requiring energy. Magnetic DESs were obtained by suspending the magnetic nanoparticle Fe2O3 in the carrier DES. All parameters affecting the extraction efficiency, such as pH, magnetic DES volume and composition, extraction time, dithizone amount, etc., were optimized for both CV and Cd(II). As a result of the optimization studies, the highest extraction efficiency for CV was achieved with a pH of 7, DES composition of 1:3 ChCl:Ph, magnetic nanoparticle Fe2O3 amount of 60 mg, and ultrasound time of 4 minutes. For Cd(II), the highest efficiency was achieved with a pH of 5, 0.1% (w/v) DTZ volume of 500 μL, DES composition of 1:3 ChCl:Ph, magnetic nanoparticle Fe2O3 amount of 80 mg, and ultrasound time of 4 minutes. Under optimum conditions, the enrichment factor (EF) was 22 and 31; the limit of detection (LOD) was 1.13 and 0.73 μg L-1, the limit of quantification (LOQ) was 3.75 and 2.43 μg L-1, and the relative standard deviation (RSD, n = 10) was 5.95% and 4.80% for CV and Cd(II), respectively. After optimizing the experimental conditions and evaluating the analytical features, the developed method was applied to a certified reference material (TMDA-61.2, Lake Ontario Water), water samples obtained from a lake and a fish farm, and various seafoods (shrimp, mussel, sea bass, sea bream, trout). The experiments resulted in high recovery values with high sensitivity and accuracy, free from matrix effects. Additionally, the greenness of the developed MDES-DLLME method for CV and Cd(II) was evaluated using ComplexGAPI, AGREE, and AGREEprep programs, and it was concluded that the method is in compliance with the principles of green chemistry according to all three programs.