Development of in-situ produced CO2 switchable fatty acid microextraction based solidification of floating organic droplet for quantification of morin and quercetin in tea, vegetable and fruit juice samples by HPLC

An in-situ produced CO2 switchable fatty acid microextraction based on solidification of floating organic droplet (In-situ-CO2-SFA-ME-SFO) was evaluated for microextraction of two antioxidant flavonoids (morin and quercetin) in tea, fruit juice and vegetable samples prior to HPLC-UV. Medium-chain fatty acids (e.g. nonanoic acid) were investigated as switchable hydrophilicity solvents via pH adjustment. Sodium carbonate (Na2CO3) was used to solubilize immiscible fatty acid in water as well as, to provide effervescence. The addition of H2SO4 into the solution led to the in-situ chemical reaction with excess Na2CO3 which resulted in effective dispersion of fatty acid through generated CO2 and separation of phases. Subsequently, solidification of the fatty acid enabled facile separation without the need for sophisticated equipment. To optimize extraction process, the effects of some important parameters on the extraction recovery were investigated. At the optimum conditions, the limits of detection (LODs) and the limits of quantification (LOQs) were found 0.5 and 1.3 µg L−1 and 1.6 and 4.3 µg L−1 for morin and quercetin respectively. The preconcentration factors were 105 while, the relative standard deviations (RSDs %) of the method were < 3.5 % for both flavonoids. The recoveries of the analytes in tea, vegetable and fruit juice samples were in the range of 95.5 and 98.2