Simultaneous preconcentration and analysis of anthraquinones based on ultrasound emulsification ionic liquid microextraction.

An ultrasensitive method of ultrasound emulsification ionic liquid microextraction (UEILME) coupled with high-performance liquid chromatography (HPLC) has been developed and introduced for the preconcentration and analysis of anthraquinone additives in cosmetic samples and five anthraquinone compounds (aloe-emodin, rhein, emodin, chrysophanol and physcion) in traditional Chinese medicines. Several parameters affecting the extraction efficiency were investigated and optimized, such as the type and amount of extraction solvent, sample pH, ultrasound time and temperature, centrifugation speed and time and ionic strength. The most favorable results were obtained using 60 mg of 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. The anthraquinones were extracted from the aqueous solution (pH 2.0) by ultrasound at 40°C for 7 min and centrifuged at 2,500 rpm for 6 min. Under optimal conditions, acceptable linearity of the five anthraquinone compounds was obtained with correlation coefficients > 0.99. The limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.01 to 0.09 µg/L and 0.05 to 0.25 µg/L, respectively. The relative standard deviations (n = 3) were less than 9.8%. Moreover, the enrichment factors ranged from 80 to 197-fold. Compared with conventional dispersive liquid-liquid microextraction, the UEILME technique exhibited lower LODs and LOQs. The results demonstrated that the UEILME coupled with HPLC is a simple, environmentally friendly, sensitive and efficient method for the extraction, concentration and analysis of anthraquinone compounds.