Ionic Liquid‐Based Polarity‐Adjustable Deep Eutectic Solvent Extraction Followed by High‐Performance Liquid Chromatography‐Diode‐Array Detection for the Determination of Liposoluble Anthraquinones in <i>Salvia miltiorrhiza</i> Bge. Root

A simple, green, and efficient ultrasound-assisted deep eutectic solvents (DESs) extraction followed by high-performance liquid chromatography-diode array detector was established to detect four liposoluble anthraquinones in Salvia miltiorrhiza Bge. root. In this study, a series of polarity-adjustable DESs were prepared using n-hexanol and tetrabutylammonium chloride, and their structure, density, viscosity, pH, and thermal stability were determined. The conditions for extraction were optimized through single-factor experiments and response surface methodology. The kinetic and thermodynamic properties associated with the ultrasound-assisted extraction of anthraquinones were investigated. The results showed that the standard curves for anthraquinones showed excellent linearity from 0.018 to 150 µg mL^-1 (r > 0.9998). The detection and quantification limits varied from 5.04 to 5.60 ng mL^-1 and 16.81 to 18.67 ng mL^-1, respectively. The recoveries were measured as 84.1%-95.1%, and the relative standard deviations were not exceeded 4.6%.