Modified dispersive solid-liquid microextraction coupled to HPLC and application of experimental design methodology to determine the trace amount of levothyroxine in human real samples

A simple, efficient and green microextraction method namely ultrasound assisted-dispersive solid-liquid microextraction based on solidification of floating organic droplet (UA-DSLME-SFOD) coupled to HPLC and UV detector was developed for preconcentration and determination of levothyroxine in human urine and serum samples. The effects of different variables on the extraction efficiency such as pH, volume of extraction solvent, amount of solid disperser, ionic strength and time of ultra-sonication were studied and optimized simultaneously using response surface methodology. For validation of the technique, its accuracy, precision, limit of detection, linearity, and sensitivity were evaluated. The calibration graph of the proposed method was linear in the range of 0.5-2000.0 ng mL− 1 with the determination coefficient (R2) of 0.9986. The relative standard deviations for 6 replicates were 1.76-3.32% (n = 6). This method provided high sensitivity, using of low toxic organic solvents, and simplicity of the extraction processes. The proposed method was successfully applied for determination of levothyroxine in human urine and serum samples.