Removal of Ionic Liquid (IL) from Herbal Materials After Extraction with IL and Comprehensive Investigation

At present, ionic liquids (ILs) are increasingly being used to extract natural products as green solvents, but their residues can lead to risks in terms of further use for the extracted herbal materials. Therefore, it is necessary to remove them with simple and effective methods. For example, after the toxic anthraquinones inPolygonum multiflorumare removed by extraction with the IL of [C4Bim][PTSA], it needs to be recovered and reused, and the useful stilbene glycosides should not suffer from obvious loss as they are the main functional components. In this study, an ultrasonic method withn-propanol was used to remove the residual [C4Bim][PTSA] in the solid powders ofPolygonum multiflorumthat had been extracted for anthraquinones. After single-factor optimization, the removal conditions were as follows: the removal temperature was 303.15 K, the solid–liquid ratio was 1:200 (w (1 g):v (200 mL)), the ultrasonic time was 40 min, and there were four operations. Under these conditions, ILs could be completely removed with almost no loss of stilbene glycosides in solid powders. After that, the IL in the extracting solution and scrubbing solution was recovered by the back-extraction method, and an IL with high purity could be obtained for reuse. The total recovery efficiency of the IL reached more than 98%. Then gas chromatography (GC) was conducted for the determination of residual ethanol andn-propanol in the solid powders ofPolygonum multiflorum, which could be used to quickly detect the contents of two organic solvents within three minutes. Besides that, the method could also be applied to the determination of residual organic solvents in the raw materials ofPolygonum multiflorum, and the results showed that the residue of ethanol andn-propanol in the solid powders were in accordance with the general provisions of the currentChinese Pharmacopoeia. According to the developed procedures and optimized conditions, the recovered IL could be reused in five runs at least. General applicability and greenness assessment for the developed process also proved that it is an ideal method, which has potential in large-scale application.