A switchable deep eutectic solvent for the homogeneous liquid-liquid microextraction of flavonoids from "Scutellariae Radix"

Deep eutectic solution elution assisted ligand affinity assay: A useful tool for the active coumarins screening from Fructus cnidii

BACKGROUND

Many of the ligand affinity analyses are presented in water environment, and the hydrophilic solution such as methanol is used for dissociating the bound compounds. The obtained dissociation solution needs to be concentrated for improving the sensitivity of the assay. However, it is not good for the analysis of hydrophobic and volatile compounds such as coumarins. The solubility of them in water environment is low. And they may be lost in the sample preparation process. In this work, a deep eutectic solvent elution assisted ligand affinity assay for the screening of active coumarins in plants was proposed.

RESULTS

For the first time, deep eutectic solvent was used as a dissociation solution for dissociating the compounds that bind with acetylcholinesterase immobilized magnetic beads. Analytes could be enriched during the phase separation process of deep eutectic solvent. The concentration of the analytes in sample solution was therefore increased. It is good for the detection of coumarins. The LOD and LOQ of the proposed assay were 0.50 (μ g/mL) and 1.50 (μ g/mL), respectively. The relative recovery of the assay was 99.4 ± 7.2 %. The intra-day and inter-day precision were 7.25 % and 6.80 %. Using the assay as a tool, the active coumarins in Fructus cnidii were analyzed. And two coumarins with acetylcholinesterase inhibition activity such as imperatorin and osthole were found.

SIGNIFICANCE

Coumarins have good solubility in the selected deep eutectic solvent, and could be enriched into hydrophobic phase during the phase separation process. The extra concentration process is not needed. Compared with traditional methods, the proposed method has the benefits of simplified operation process, high sensitivity, and is friendly to the volatile and hydrophobic compounds.

Determination of polychlorinated biphenyls in water by CO2-responsive switchable deep eutectic solvent based homogeneous liquid-liquid microextraction

A homogeneous liquid-liquid microextraction technique based on switchable deep eutectic solvent (SDES-HLLME), combined with gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS), was developed for the extraction and analysis of 16 polychlorinated biphenyls (PCBs) in water samples. CO2-responsive switchable deep eutectic solvent (SDES), which consists of monoethanolamine (MEA) being used as a hydrogen bond acceptor (HBA) and 3-methoxyphenol (3-MP) being used as a hydrogen bond donor (HBD), was used as the extractant, thus providing an environmentally friendly alternative to conventional toxic organic solvents. The study systematically investigated the effects of various parameters on extraction efficiency, including the type and volume of SDES, vortexing duration, CO2 bubbling time, centrifugation rate and time, ionic strength. Optimal extraction conditions were identified as follows: 40.0 μL of SDES, vortexing for 40.0 s, CO2 bubbling for 2.0 min, 5.0 % (w/v) salt concentration, a centrifugation rate of 5000 rpm, and a centrifugation duration of 3.0 min. Under these optimal conditions, the method exhibited a linear range of 0.1-300 ng·mL-1, with limits of detection (LODs) and quantification (LOQs) ranging from 0.003 to 0.096 ng·mL-1 and 0.009 to 0.321 ng·mL-1, while the relative standard deviation (RSD) <7.98 %. Finally, this method was successfully applied to determine the concentrations of 16 PCBs in various environmental water samples, yielding satisfactory recovery rates. This method provides a green, convenient and accurate new idea in the field of HLLME research.

Handshake of deep eutectic solvent and ionic liquid: Two liquid-liquid microextraction procedures for plant analysis

Plants are subjects of interest due to the secondary metabolites in their extracts which are promising as new pharmaceuticals. Phytochemistry do not have united system of sample preparation or analysis still due to different structure of plant cells, wide broad range of chemical properties and concentrations of bioactive compounds. Such challenges can be addressed in a green chemistry manner using new approaches through smart materials in routine monitoring and researches. Liquid smart materials, such as ionic liquids (ILs) and deep eutectic solvents (DESs) are attractive due to flexible properties, lots of extraction approaches, recycle potential, and direct compatibility with powerful analytical methods. In this study DES-based microextraction procedure with pH-switching was developed. Four choline chloride DESs were suggested as selective extraction phases for polar compounds from acetonitrile extracts. Method was successfully tested on four plants (Iris sibirica L., Hypericum perforatum L., Scutellaria baicalensis G, Citrus reticulata B.). Developed procedure was optimized and validated for the choline chloride - urea (1:2 mol/mol) DES that demonstrated better results in extraction. LOD for rutin was found as 0.05 mg ml-1. For low-polar compound, imidazolium ionic liquid-based dispersive liquid-liquid microextraction procedure was developed. 1-hexyl-3-methylimidazolium salts have demonstrated desired selectivity. The main factors influencing the extraction efficiency have been identified and optimized by design of experiment on two model plants (Iris sibirica L. and Scutellaria baicalensis G.). Validation procedures were done for thymol. LOD for thymol was found as 0.021 mg ml-1. The methods were compared with each other and traditional methanol extraction. The selectivity of the smart materials supports each other, usage of such extraction phases provides same or better results as obtained with methanol.

Ultrasound assisted upper critical solution temperature type switchable deep eutectic solvent based liquid-liquid microextraction for the determination of triazole in water

BACKGROUND

The use of pesticides to protect crops has long been an important measure to provide healthy and safe agricultural products, but excess pesticides flow into fields and rivers, causing environmental pollution. Earlier methods utilizing organic solvent liquid-liquid microextraction for pesticide residue detection were not environmentally friendly. Therefore, it is significant to find a greener and more convenient detection method to determine pesticide residues.

RESULTS

A new method was established to detect three triazole fungicides (TFs), including myclobutanil, epoxiconazole and tebuconazole, in environmental water samples. And the determination was conducted using a high-performance liquid chromatography with the ultraviolet detector (HPLC-UV). The switchable deep eutectic solvent (SDES) can be reversibly switched between hydrophilic and hydrophobic states through temperature modulation. Additionally, the method exhibited excellent linearity for all target analytes within the concentration range of 10-2000 μg L-1, with satisfactory R2 values (≥0.9975). The limits of detection (LODs) ranged from 2.3 to 2.6 μg L-1, and the limits of quantification (LOQs) ranged from 7.8 to 8.7 μg L-1. The accuracy of the method was assessed through intra-day and inter-day precision tests, yielding relative standard deviations (RSDs) in the ranges of 2.8%-6.7% and 2.2%-7.5%, respectively. Density functional theory (DFT) results indicated that hydrogen bonding is a significant factor affecting the binding of DES with triazoles. Three different green assessment tools were used to prove that the SDES-HLLME method had good greenness and broad applicability.

SIGNIFICANCE

This is a homogeneous liquid-liquid microextraction (HLLME) method based on the upper critical solution temperature (UCST) type switchable deep eutectic solvent program, which can complete the extraction within a few minutes without dispersant. In terms of pesticide detection, the analytical method is simple and more conducive to environmental protection.

A Comprehensive Review on Deep Eutectic Solvents: Their Current Status and Potential for Extracting Active Compounds from Adaptogenic Plants

Deep eutectic solvents (DESs) have attracted attention from researchers as novel compounds for extracting active substances because of their negligible toxicity, polarity, and ability to be tailored depending on the experiment. In this review, we discuss deep eutectic solvents as a promising medium for the extraction of adaptogenic compounds. In comparison to traditional methods, extraction with the use of DESs is a great alternative to the excessive usage of harmful organic solvents. It can be conducted in mild conditions, and DESs can be designed with different precursors, enhancing their versatility. Adaptogenic herbs have a long medicinal history, especially in Eastern Asia. They exhibit unique properties through the active compounds in their structures, including saponins, flavonoids, polysaccharides, and alkaloids. Therefore, they demonstrate a wide range of pharmaceutical effects, such as anti-inflammatory, antibacterial, and anticancer abilities. Since ancient times, many different adaptogenic herbs have been discovered and are well known, including Panax ginseng, Scutellaria baicalensis, and Schisandra chinensis. Active compounds can be extracted using standard methods, such as hydrolyzation, maceration, and conventional reflux extraction. However, due to the limitations of classical processing technologies, there has been a need to develop new and eco-friendly methods. We focus on the types of solvents, extraction efficiency, properties, and applications of the obtained active compounds. This review highlights the potential of DESs as eco-friendly alternatives for extracting bioactive compounds.

Switchable deep eutectic solvent as green and efficient media for liquid-phase microextraction of phenoxyacetic acid herbicides in water and food matrices

In this work, a switchable deep eutectic solvent (SDES) based on fatty acid and polyetheramine ion pair was prepared for liquid-phase microextraction (LPME) of phenoxyacetic acid herbicides in drinking water, beverage and honey matrices. The as-synthesized SDES equipped with an interesting characteristic of fast and reversible polarity switching, achieving homogeneous extraction and rapid bi-phase separation simultaneously. Several key parameters affecting the extraction performance were investigated comprehensively by Box-Behnken design. Under the optimal conditions, the method exhibited excellent linearity (15-4000 μg L-1), low detection limits (3-5 μg L-1), desirable precision (RSD < 8.1 %), and satisfactory recovery (72.6-98.7 %). More importantly, the introduction of SDES can simplify the pre-treatment procedure, shorten extraction time (4 min), and avoid the usage of traditional organic solvent during the whole extraction process. In addition, the switching mechanism of SDES was characterized by FT-IR and 1H NMR, and the forming mechanism of SDES was investigated using density-functional theory. The green of the method was estimated using the analytical ecological scale, the analytical green calculator, and the green analytical procedure index. The cytotoxicity of SDES was investigated and the result displayed that toxicity of the SDES was very low with the EC50 > 500 mg/L. Therefore, the proposed method was green and efficient and revealed considerable application prospects for the extraction of trace analytes from complex materials.

Supramolecular deep eutectic solvent: a powerful tool for pre-concentration of trace metals in edible oil

The utilization of supramolecular deep eutectic solvent eddy-assisted liquid-liquid microextraction utilizing 2-hydroxypropyl β-cyclodextrin (SUPRADES) has been identified as a successful method for pre-enriching Cu, Zn, and Mn in vegetable oil samples. Determination of each element was conducted by inductively coupled plasma optical emission spectrometry (ICP-OES) after digestion of metal-enriched phases. Various parameters were examined, including the composition of SUPRADES species [2HP-β-CD: DL-lactic acid], a cyclodextrin mass ratio of 20 wt%, a water bath temperature of 75 °C, an extractor volume of 800 μL, a dispersant volume of 50 μL, and an eddy current time of 5 min. Optimal conditions resulted in extraction rates of 99.6% for Cu, 105.2% for Zn, and 101.5% for Mn. The method exhibits a broad linear range spanning from 10 to 20,000 μg L-1, with determination coefficients exceeding 0.99 for all analytes. Enrichment coefficients of 24, 21, and 35 were observed. Limits of detection ranged from 0.89 to 1.30 μg L-1, while limits of quantification ranged from 3.23 to 4.29 μg L-1. The unique structural characteristics of the method enable the successful determination of trace elements in a variety of edible vegetable oils.

Functionalized magnetic nanomaterials as recyclable adsorbents for efficient flavonoid enrichment in Scutellaria Radix

A magnetic composite (Fe3O4@SiO2@PNIPAM-co-NHMA) with high adsorption capacity and recoverability was developed for the enrichment and determination of flavonoids in Scutellaria Radix (SR). A magnetic solid-phase extraction (MSPE) technique using Fe3O4@SiO2@PNIPAM-co-NHMA absorbent in combination with high-performance liquid chromatography (HPLC) was developed for selectively enrichment and determination of the biologically active flavonoids in the aqueous extract of SR, including baicalein, baicalin, wogonoside and wogonin. Under the optimized experimental conditions, the magnetic adsorbent could adsorb up to 77.0 ± 0.98 % - 98.15 ± 0.15 % of four representative flavonoids from SR, with elution rates varying from 55.10 ± 0.25 % to 91.94 ± 1.85 %. The limits of detection (LOD) and limits of quantitation (LOQ) were 0.01-0.35 μg/mL and 0.03-0.98 μg/mL, respectively. In addition, it remained effective after six replicates, demonstrating its potential as a recoverable adsorbent for enriching flavonoids in traditional Chinese medicine.

Hydroxyl-rich ferrofluid for efficient liquid phase microextraction of cinnamic acid derivatives in traditional Chinese medicine

In this study, a hydroxyl-rich ferrofluid was prepared by dispersing silica-coated magnetic nanoparticles into a methyltrioctylammonium chloride-glycerol deep eutectic solvent and then employed in the preconcentration of trace-level of cinnamic acid derivatives (caffeic acid, p-hydroxycinnamic acid, ferulic acid, and cinnamic acid) in traditional Chinese medicine prior to high-performance liquid chromatography analysis. The structures of the synthesized materials were characterized by X-ray diffraction and infrared spectroscopy. The experimental parameters affecting the extraction performance, such as deep eutectic solvent composition, dosage of ferrofluid, pH of aqueous sample solution, salt concentration, extraction time, type, and volume of desorption solvent, were studied and optimized. Under the optimum conditions, the enrichment factors of four cinnamic acid derivatives were in the range of 107-114. Low detection limits (0.2-0.9 ng/mL), good precisions (relative standard deviations 1.2%-9.5%), and satisfactory recoveries (96.0%-104.7%) were achieved. Subsequently, the possible microextraction mechanism of the proposed method was explored and elucidated. It showed that the prepared ferrofluid is easily dispersed in the aqueous sample and achieved recovery after the extraction. The developed approach is a simple, convenient, and efficient method for preconcentration and determination of cinnamic acid derivatives in complex matrices.

Deep eutectic solvents in sample preparation and determination methods of pesticides: Recent advances and future prospects

This review summarizes recent advances of deep eutectic solvents (DESs) in sample preparation and determination methods of pesticides in food, environmental, and biological matrices since 2019. Emphasis is placed on new DES categories and emerging microextraction techniques. The former incorporate hydrophobic deep eutectic solvents, magnetic deep eutectic solvents, and responsive switchable deep eutectic solvents, while the latter mainly include dispersive liquid-liquid microextraction, liquid-liquid microextraction based on in-situ formation/decomposition of DESs, single drop microextraction, hollow fiber-liquid phase microextraction, and solid-phase microextraction. The principles, applications, advantages, and limitations of these microextraction techniques are presented. Besides, the use of DESs in chromatographic separation, electrochemical biosensors, fluorescent sensors, and surface-enhanced Raman spectroscopy are discussed. This review is expected to provide a valuable reference for extracting and detecting pesticides or other hazardous contaminants in the future.

A modified strategy to improve the dissolution of flavonoids from Artemisiae Argyi Folium using ultrasonic-assisted enzyme-deep eutectic solvent system

In this study, enzyme-deep eutectic solvent-assisted ultrasonic extraction technique (EnDUE) was developed for the efficient dissolution of flavonoids from Artemisiae Argyi Folium. The extraction results of Artemisiae Argyi Folium flavonoids (quercetin, luteolin, and isorhamnetin) were used as indicators to investigate the influencing factors through single factor experiment, Placket-burman design, and Box-behnken design, so as to obtain satisfactory yields. After systematic optimization, the optimal conditions for extraction of the target flavonoids were: Choline chloride/1,4-butanediol with a water content of 25%, cellulase+pectinase with a concentration of 1.6%, solid-liquid ratio of 1/32 g/mL, pH of 4.2, ultrasonic frequency of 80 kHz, ultrasonic power of 160 W, ultrasonic temperature of 40 °C, and ultrasonic time of 25 min, respectively, which derived a total yield of 8.06 ± 0.29 mg/g. Compared with the reference techniques, the proposed EnDUE technique showed significant advantages in the yield and extraction efficiency of flavonoids. In addition, after preliminary purification, the Artemisiae Argyi Folium flavonoids showed good antioxidant activity. Deep eutectic solvent (DES) can degrade the cell wall components and increase the action site of enzyme, and enzyme can promote the penetration of DES into the cell wall matrix, which is mutually beneficial to the dissolution of intracellular components. Therefore, the extraction technique proposed in this work (EnDUE) greatly promotes the dissolution of flavonoids from Artemisiae Argyi Folium, and provides theoretical support for the further application of plant flavonoids.

An effervescence-assisted switchable deep eutectic solvent based liquid-phase microextraction of triazole fungicides in drinking water and beverage

A new effervescence-assisted switchable deep eutectic solvent-based liquid phase microextraction (EA-SDES-LPME) combined with HPLC-UV was developed for determination of common triazole fungicides in drinking water and beverages, including myclobutanil, flusilazole, hexaconazole and bitertanol. The alternative extraction solvent was prepared with hexafluoroisopropanol and dipropylamine with the merits of time-saving, easy to collect and cost-effectiveness. The SDES can be reversibly switched between hydrophilic and hydrophobic states by pH adjustment. The homogeneous extraction was achieved under the hydrophilic form of SDES, and the bi-phase separation was obtained easily by adjusting pH value to restore the original hydrophobicity. Moreover, the characterization of SDES was investigated by FTIR and 1H NMR. The main variables affecting extraction efficiency were optimized in detail. Under the optimal conditions, the proposed method shows desirable precision (RSDs less than 18.5%) and acceptable recovery (72.6-95.4%). The lower limits of detection and limits of quantitation were found to be in the range of 1-2 μg L-1 and 5-10 μg L-1, respectively. The formation mechanism of SDES and the extraction mechanism for target analytes were investigated by density functional theory. The proposed methodology was simplicity, sensitive, time-saving and successfully applied to determine triazole fungicides in drinking water and beverages, making it an alternative technique for the analysis of trace analytes with satisfactory sensitivity.

Determination of Flavonoid Compounds in Shanxi Aged Vinegars Based on Hydrophobic Deep Eutectic Solvent VALLME-HPLC Method: Assessment of the Environmental Impact of the Developed Method

This research presents a novel, eco-friendly, vortex-assisted liquid-liquid microextraction (VALLME) approach, integrating hydrophobic deep eutectic solvents (DESs) with HPLC for the identification and quantification of nine specific flavonoids in Shanxi aged vinegar (SAV). The parameters of DES-VALLME, including the ratio of trioctylmethylammonium chloride to 1,4-butanediol (1:6), DES volume (150 μL), vortex duration (5 min), the concentration of NaCl (0.40 g), and centrifugation time (10 min), were optimized to achieve the maximum extraction efficiency of target substances. Under these optimal conditions, quantitative analyses performed via HPLC demonstrated a broad linear range of 0.20-50.00 μg/mL and correlation coefficients (r²) greater than 0.9944 for all nine calibration curves. The limits of detection (LOD) and limits of quantitation (LOQ) were 0.09-0.18 μg/mL and 0.30-0.60 μg/mL, respectively, ensuring high sensitivity. The relative standard deviations for intra-day and inter-day variability were within the acceptable range, 2.34-3.77% and 3.04-4.96%, respectively, demonstrating the method's reliability. The recovery rates ranged from 85.97% to 108.11%, underscoring the method's precision. This technique exhibited a significant enrichment effect (enrichment factor: 43 to 296) on SAV flavonoids. Notably, the eco-friendliness of this procedure was evaluated using the Analytical Eco-Scale, Green Analytical Procedure Index, and Analytical Greenness Metric. The results suggested that this technique is a viable green alternative to traditional flavonoid determination methods in SAV. In summary, this novel method provides a theoretical basis for assessing flavonoid content in SAV samples and tracing SAV products. This contribution has significant implications for enhancing analytical techniques in food chemistry and environmental science and the sustainable development of the food industry.