Determination of methylene blue and sunset yellow in wastewater and food samples using salting-out assisted liquid–liquid extraction

In this research work a simple and very fast salting-out assisted liquid–liquid extraction (SALLE) followed by UV–vis spectrphotometric method was developed and applied for determination of methylene blue and sunset yellow in wastewater and food samples. Water-miscible extraction solvent (4.5 mL acetonitrile) was added to aqueous solution (5.5 mL) for formation of a homogeneous solution. To the mixture solution, suitable amount of (NH4)2SO4 was added, the mixture solution was shaken until the salt was dissolved, and then it was separated into two clear phases easily and rapidly. The target analytes in the sample was extracted into the water-miscible extraction solvent. After extraction, the analytes in the organic phase was determined by spectrphotometric method using the analytical wavelengths of 417 nm, 656 nm for sunset yellow and methylene blue, respectively. The influences of effective parameters such as salt (type and amount), water-miscible organic solvent, phase volume ratio, and pH of sample solution were studied and optimized. Under optimized experimental conditions, calibration plots were found to be linear in the range of 0.2–7.0 mg/L, and 0.4–15.0 mg/L for methylene blue and sunset yellow, respectively, with coefficient of determinations more than 0.996. The limits of detection were 0.06 and 0.07 mg/L for methylene blue and sunset yellow, respectively. The limits of quantification were 0.20 mg/L and 0.25 mg/L for methylene blue and sunset yellow, respectively The proposed procedure was successfully applied to the determination of analytes in spiked samples with satisfactory results. The relative recoveries ranged over 90.2–106.0%, with relative standard deviations varying from 1.1% to 3.8%.