Novel hydrophobic deep eutectic solvents for ultrasound-assisted dispersive liquid-liquid microextraction of trace non-steroidal anti-inflammatory drugs in water and milk samples

In the present study, several novel and natural hydrophobic deep eutectic solvents (HDESs) were prepared, and one of the HDESs composed of guanidinium chloride and thymol was advantageously used to develop an ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) method combined with high-performance liquid chromatography for the determination of four non-steroidal anti-inflammatory drugs (NSAIDs). Several important parameters influencing extraction efficiency were investigated and optimized, including the type and volume of HDES, ultrasound time, solution pH and the amount of salt addition. Under optimal experimental conditions, the method showed good linearity with the determination coefficients (R2) of 0.994–0.999 in the linear range of 5–2000 μg/L, low limits of detection of 0.5–1 μg/L and acceptable recoveries in the range of 79.42%–107.52%. The proposed method was successfully applied for the pretreatment of trace NSAIDs in real water and milk samples, and the results demonstrated the potential of the synthesized HDES for the extraction and determination of contaminants in aqueous samples.