A new ultrasound-assisted liquid-liquid microextraction method utilizing a switchable hydrophilicity solvent for spectrophotometric determination of nitrite in food samples

A new and sustainable switchable hydrophilicity solvent-based ultrasound-assisted liquid-liquid microextraction (SHS-UA-LLME) procedure was proposed to extract and determine nitrite in heat processed foods using a spectrophotometer. Three switchable hydrophilicity solvents (SHS-1, SHS-2, and SHS-3) were prepared and used as an extraction solvent for nitrite by mixing N,N-dimethylcyclohexylamine (DMCA), trethylamine (TEA), and N,N-dimethylbenzylamine (DMBA) with water in a 1:1 molar ratio. Protonation of the SHSs were achieved by using dry ice (solid CO₂) to make it water soluble, and addition of NaOH converted it back to its original non-ionic state for phase separation and subsequent extraction of nitrite. Ultrasound was applied to increase the extraction capability of the nitrite in the samples. Various analytical parameters including the pH of the sample solution, SHS types and their volumes, extraction time, and sample volume were optimized. The effects of matrix ions were also studied. Limit of detection and limit of quantification were found 0.1 µg L^–1 and 0.3 µg L^–1, respectively. The linear range and preconcentration factor were 0.3–600 µg L^–1 and 250, respectively. The proposed SHS-UA-LLME was applied to the heat-processed foods with the standard addition method and recoveries were achieved in the range of 91–99%. The factorial design was also used and access the impact of factor and fitness of the model using response surface methodology. The innovation of the proposed SHS-UA-LLME was demonstrated the usability of SHSs for the selective determination and extraction of nitrite by multivariate statistical analysis. In addition, the proposed SHS-UA-LLME does not require heating and centrifugation steps, which provides superiority in terms of cost and time compared to other similar methods.