Baokun Tang

Recent developments in deep eutectic solvents in chemical sciences

In recent years, deep eutectic solvents (DESs) have been considered green solvent alternatives to conventional solvents and have attracted considerable attention. With an in-depth understanding of the common and novel properties of DESs, many of them have been prepared and applied to various areas of chemistry. To summarize the full-scale development of DESs, we reviewed this field from its inception. This review summarizes the general trends in the development of DESs and evaluates the major aspects of DESs, such as their properties, preparations, and applications. This work is expected to be helpful for the further development of DESs based on a summary of the fundamental research in the field.Graphical Abstract

Application of ionic liquid for extraction and separation of bioactive compounds from plants

In recent years, ionic liquids (ILs), as green and designer solvents, have accelerated research in analytical chemistry. This review highlights some of the unique properties of ILs and provides an overview of the preparation and application of IL or IL-based materials to extract bioactive compounds in plants. IL or IL-based materials in conjunction with liquid-liquid extraction (LLE), ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), high performance liquid chromatography (HPLC) and solid-phase extraction (SPE) analytical technologies etc., have been applied successfully to the extraction or separation of bioactive compounds from plants. This paper reviews the available data and references to examine the advantages of IL and IL-based materials in these applications. In addition, the main target compounds reviewed in this paper are bioactive compounds with multiple therapeutic effects and pharmacological activities. Based on the importance of the targets, this paper reviews the applications of ILs, IL-based materials or co-working with analytical technologies. The exploitation of new applications of ILs on the extraction of bioactive compounds from plant samples is expected to increase.

Application of deep eutectic solvents in the extraction and separation of target compounds from various samples

Deep eutectic solvents, as a new type of eco-friendly solvent, have attracted increasing attention in chemistry for the extraction and separation of target compounds from various samples. To summarize the application of deep eutectic solvents, this review highlights some of the unique properties of deep eutectic solvents and deep-eutectic-solvent-based materials, as well as their applications in extraction and separation. In this paper, the available data and references in this field are reviewed to summarize the application developments of deep eutectic solvents. Based on the development of deep eutectic solvents, the exploitation of new deep eutectic solvents and deep-eutectic-solvent-based materials are expected to diversify into extraction and separation.

Application of ionic liquid in liquid phase microextraction technology

Ionic liquids (ILs) are novel nonmolecular solvents. Their unique properties, such as high thermal stability, tunable viscosity, negligible vapor pressure, nonflammability, and good solubility for inorganic and organic compounds, make them excellent candidates as extraction media for a range of microextraction techniques. Many physical properties of ILs can be varied, and the structural design can be tuned to impart the desired functionality and enhance the analyte extraction selectivity, efficiency, and sensitivity. This paper provides an overview of the applications of ILs in liquid phase microextraction technology, such as single-drop microextraction, hollow fiber based liquid phase microextraction, and dispersive liquid-liquid microextraction. The sensitivity, linear calibration range, and detection limits for a range of target analytes in the methods were analyzed to determine the advantages of ILs in liquid phase microextraction.

Application of Deep Eutectic Solvents as Additives in Ultrasonic Extraction of Two Phenolic Acids from Herba Artemisiae Scopariae

This paper reports the extraction of two phenolic acids from Herba Artemisiae Scopariae using deep eutectic solvents that were synthesized with various salt and hydrogen bond donors. The optimal conditions were found to be 50% of a synthesized deep eutectic solvent from tetramethyl ammonium chloride and urea (1:4) mixed with methanol/water (60:40, v/v). Phenolic acid extraction was optimized using an ultrasonic power of 89 W for 30 min with a solid/liquid ratio of 1:10. Under the optimized conditions, good calibration curves were observed at phenolic acid concentrations ranging from 10.0 to 500.0 µg/mL. The method recovery ranged from 97.3% to 100.4%, and the inter-day and intra-day relative standard deviations were less than 5%. Under the optimal extraction conditions, the amounts of chlorogenic acid and caffeic acid extracted from Herba Artemisiae Scopariae were 9.35 mg/g and 0.31 mg/g, respectively.

Extraction of catechin compounds from green tea with a new green solvent

An emerging green solvent called a deep eutectic solvent(DES) was applied to the extraction and determination of catechin(C), (+)epicatechin gallate(ECG) and (−)epigallocatechin gallate(EGCG) from Chinese green tea. After evaluating different combinations of them by extraction methods and DESs, a DES-based extraction method was established and optimized by a systematic investigation of the influencing factors. As a result, a total of 3.629, 35.25 or 114.2 mg/g catechin, (+)epicatechin gallate or (−)epigallocatechin gallate were extracted respectively under optimal conditions with extraction efficiencies of 82.7%, 92.3% and 97.0%, respectively. By comparing with other common used solvents for extracting catechin compounds, DESs were proved to be potential extraction solvents for bioactive ingredients.

A Green Deep Eutectic Solvent-Based Ultrasound-Assisted Method to Extract Astaxanthin from Shrimp Byproducts

The extraction of valuable compounds from waste products using green and inexpensive solvents is a significant strategy for sample preparation. Accordingly, in the present study, the use of deep eutectic solvents, an emerging green approach, was used to extract astaxanthin, a well-known and widely-used antioxidant, from shrimp byproducts. After evaluating different combinations of extraction conditions and deep eutectic solvents, an ultrasonication method was established and optimized by a systematic investigation of the influencing factors. A comparison of the amount of astaxanthin (102 μg g− 1 ) extracted using a traditional organic solvent, ethanol, showed that more astaxanthin (146 μg g− 1 ) was obtained using the reported eco-friendly method. The excellent properties of deep eutectic solvents highlight their advantages as promising inexpensive green solvents for the extraction and determination of a range of bioactive compounds from natural products.

Simultaneous Extraction of Flavonoids from Chamaecyparis obtusa Using Deep Eutectic Solvents as Additives of Conventional Extractions Solvents

Three flavones (quercetin, myricetin and amentoflavone) were extracted from Chamaecyparis obtusa leaves using deep eutectic solvents (DESs) as additives to conventional extractions solvents. Sixteen DESs were synthesized from different salts and hydrogen bond donors. In addition, C. obtusa was extracted under optimal conditions of methanol as the solvent in the heating process (60°C) for 120 min at a solid/liquid ratio of 80%. Under these optimal conditions, a good linear relationship was observed at analyte concentrations ranging from 5.0 to 200.0 μg/mL (R(2) > 0.999). The extraction recovery ranged from 96.7 to 103.3% with the inter- and intraday relative standard deviations of <4.97%. Under the optimal conditions, from C. obtusa, the quantities of quercetin, myricetin and amentoflavone extracted were 325.90, 8.66 and 50.34 µg/mL, respectively. Overall, DESs are expected to have a wide range of applications.

Examination of 1-methylimidazole series ionic liquids in the extraction of flavonoids from Chamaecyparis obtuse leaves using a response surface methodology

Ionic liquids (ILs) are a new type of reagent that has accelerated research in extraction technology. On the other hand, few studies have systematically applied 1-methylimidazole ([MIM]) series ILs to the extraction of bioactive compounds from plants. In this study, [MIM] series ILs were used to extract four bioactive flavonoids, such as dihydrokaempferol, quercitrin, amentoflavone and myricetin, from Chamaecyparis obtuse (CO) leaves. First, a screen of the extraction method and solvent revealed the [MIM] series ILs to be suitable as additives in methanol in Soxhlet extraction. Second, an examination of a range of cations and anions of [MIM] series ILs for extraction revealed 1-decyl-3-methylimidazolium bromide ([DMIM][Br]) to be the best selection as an additive in methanol for the Soxhlet extraction of flavonoids from (CO) leaves. Finally, some factors of extraction, such as temperature, time and amount of samples, were examined systematically using a response surface methodology (RSM). Based on the above optimization, 2.41, 3.47, 0.76 and 3.15mg/g of dihydrokaempferol, quercitrin, amentoflavone and myricetin, respectively, were extracted from 15g of CO leaves by 2.5mgmL(-1) of [DMIM][Br] as additives in 200mL of methanol in Soxhlet extraction at 200°C for 8h. This study highlights the potential of [MIM] series ILs as promising reagents for the extraction of bioactive compounds from plants.

Solid-Phase Extraction Combined with Dispersive Liquid-Liquid Microextraction for the Determination of Three Benzimidazole Pesticides (Carbendazim, Thiabendazole, and Thiophanate-Methyl) in Tomatoes

A simple, inexpensive, and reliable analytical method was developed to determine the benzimidazole residues in tomato using high performance liquid chromatography (HPLC). Sample pretreatment using solid-phase extraction (SPE) to remove the matrix and dispersive liquid–liquid microextraction (DLLME) to enrich the analytes was performed. For SPE, different sorbents and different elution processes were tested. For DLLME, the parameters affecting the extraction efficiency, such as the type and volume of extraction solvent, type and volume of the elution solvent (disperser solvent), pH, and salt addition, were examined and optimized. The method combining the advantages of SPE and DLLME showed higher selectivity and sensitivity than the conventional extraction method, and was applied successfully to determine trace levels of the benzimidazoles pesticide in tomatoes.