application and optimization of microwave-assisted extraction and dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of oleuropein and hydroxytyrosol in olive pomace

In the present study, a new method based on microwave-assisted extraction and dispersive liquid–liquid microextraction (mae–dllme) followed by high-performance liquid chromatography (hplc) was proposed for the separation and determination of oleuropein (ole) and hydroxytyrosol (hyt) from olive pomace samples. the effective factors in the mae–dllme process such as microwave power, extraction time, the type and volume of extraction, and dispersive solvents were studied and optimized with the aid of response surface methodology (rsm) based on a central composite design (ccd) to obtain the best condition for ole and hyt extraction. at the optimized conditions, parameter values were 220 w microwave power, 12 min extraction time, 60 μl extracting solvent, and 500 μl dispersive solvent. the calibration graphs of the proposed method were linear in the range of 10–500,000 μg l−1, with the coefficient of determination (r2) higher than 0.99 for ole and hyt. repeatability of the method, described as the relative standard deviation (rsd), was 4.12–5.63% (n = 6). the limits of detection were 35 and 20 μg l−1 for ole and hyt, respectively. the recoveries of these compounds in the spiked olive pomace sample were from 93 to 98%. the proposed method, mae–dllme–hplc–uv, was an accurate, rapid, and reliable method when compared with previous methods.