Application of instantaneous nebulization dispersive liquid-phase microextraction combined with HPLC for the determination of chalcone and isoflavone in traditional Chinese medicines.

A simple and rapid instantaneous nebulization dispersive liquid-phase microextraction method was developed, and combined with high-performance liquid chromatography for determination of the contents of seven analytes in traditional Chinese medicines. In this study, using the sprinkler device to achieve instantaneous synchronous dispersion and extraction, only one spray can rapidly achieve the concentration and enrichment of seven kinds of chalcone and isoflavones. The key factors affecting the extraction efficiency were optimized including the type and volume of extractant, the pH and salt concentration of the sample phase, and the number of dispersion. Under the optimal conditions, the enrichment factor of the target analytes ranged from 103.1 to 180.9, with good linearity and correlation coefficients above 0.9970. The limits of detection ranged from 0.02 to 0.15 ng/mL, with good accuracy (recoveries 91.1 to 108.9%) and precision (relative standard deviations 1.5-7.1%). This method has short extraction time (2 s), low organic solvent consumption and high enrichment effect, so it has a wide application prospects.

Dispersive liquid-liquid microextraction based on a supramolecular solvent followed by high-performance liquid chromatographic analysis of lignans in Forsythiae Fructus.

A supramolecular solvent-based dispersive liquid-liquid microextraction was proposed for the extraction and determination of lignans in Forsythiae Fructus combined with high-performance liquid chromatography. The supramolecular solvent, consisting of tetrabutylammonium bromide and n-hexanol, was mixed with the sample solution to extract the analytes by a vortex. After accomplishing the extraction, the extraction phase was separated by centrifugation and collected for high-performance liquid chromatography analysis. In this work, the important extraction variables such as the type and amount of extraction solvent, pH and salt amount in the sample phase, and extraction time were optimized. The synthesis of supramolecular solvent was studied and its microstructure was characterized by transmission electron microscopy. Under the optimal conditions, the analytes' enrichment factors were between 6 and 170 for the proposed procedure. Satisfactory linear ranges (r ≥ 0.99), detection limits (0.025-0.4 ng/ml), precisions (< 9.2%), and accuracies (recoveries: 96.5%-104.8%) were obtained. The method has been successfully applied to the preconcentration of lignans in Forsythiae Fructus with simple and rapid operation, low cost, and environmental friendliness.

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

A homogeneous liquid-liquid microextraction (HLLME) was established based on a switchable deep eutectic solvent (DES) for the preconcentration and determination of six flavonoids with different polarity in "Scutellariae Radix" combined with high performance liquid chromatography (HPLC). A switchable DES composed of N,N-dimethylethanolamine (DMEA) and heptanoic acid was used as an extraction solvent in the HLLME method, which was miscible thoroughly with the aqueous sample phase initially, and then underwent rapid phase transition induced by the addition of an inorganic acid. After the extraction, the upper hydrophobic layer was recovered for HPLC analysis. Different experimental parameters were optimized, and the optimal extraction conditions were as follows: the switchable DES extraction phase, 90 µL of DMEA-heptanoic acid (1:1 mole ratio); phase-switching trigger, 100 µL of 5 mol/L HCl; 10% (w/v) of salt concentration in sample phase; extraction time, 0.3 min. Furthermore, the structures of the switchable DES and the upper hydrophobic layer were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and differential scanning calorimetry to illustrate the phase-switching mechanism of the extraction phase during the extraction process. Under the optimized conditions, the enrichment factors for six target analytes were between 0.4 and 104. The calibration curves were linear (r≥0.9866) in the range of 0.033-8.65 mg/L for scutellarin, 0.022-5.77 mg/L for baicalin, 0.0033-0.865 mg/L for scutellarein and wogonoside, and 0.0022-0.577 mg/L for baicalein and wogonin, respectively. Low detection limits (≤8.0 × 10-3 mg/L) and quantification limits (≤2.4 × 10-2 mg/L) as well as good precisions (relative standard deviations lower than 9.2%) and acceptable accuracies (spiked recoveries 89.3-114.4%) were also obtained. The proposed method is a simple, fast, and eco-friendly sample pretreatment method.

Crystal film accelerated solvent microextraction (CF-ASME) for determination of flavonoids in natural products combined with high performance liquid chromatography.

A simple and efficient crystal film accelerated solvent microextraction (CF-ASME) technique was developed. In this study, the polyethylene pipe (PEP) with excellent comprehensive performance was used as the carrier of the extraction solvent, on which the crystal film was cured to improve its extraction capacity. The cured PEP was directly immersed in the sample phase solution to enrich the flavonoids (myricetin, quercetin, isorhamnetin, chrysin and kaempferide) in natural products. In addition, the extraction mechanism of the technique was elucidated. The important extraction variables were optimized including extraction solvent, the amount of NaCl required for crystal film preparation, salt concentration and pH of sample phase, stirring rate, extraction time, and volume of sample phase. Under the optimal conditions, the flavonoids were effectively enriched with the enrichment factors of 39.9-146.9 and they obtained good linearity with correlation coefficients higher than 0.99. The limits of detection were ranged between 0.5 and 30 ng/mL. Satisfactory accuracies (recoveries 89.4-104.8%) and precisions (relative standard deviations 5.8-11.2%) were also obtained. The proposed method was successfully applied for extraction and determination of flavonoids in natural products. Compared with the general accelerated solvent extraction methods, CF-ASME is simple to operate, green, high enrichment efficiency, which has a good application prospect.

Preconcentration of liposoluble constituents in Salvia Miltiorrhiza using acid-assisted liquid phase microextraction based on a switchable deep eutectic solvent.

A switchable deep eutectic solvent-based liquid-phase microextraction was proposed and applied to the preconcentration and determination of liposoluble quality-markers of diterpenoid quinones (dihydrotanshinone I, cryptotanshinone, tanshinone I, and tanshinone IIA) in traditional Chinese medicine coupled with high performance liquid chromatography-ultraviolet detection. In the procedure, the hydrophilic deep eutectic solvent of diethanolamine-hexanoic acid (molar ratio 1:1) was prepared and added into the sample phase as an extractant, and a homogeneous solution was formed under slight vortex stirring. After the addition of HCl solution, the deep eutectic solvent miscible with the sample phase was converted to hydrophobic form, and a cloudy solution was generated. Then, the upper hydrophobic layer enriching the target analytes was collected through centrifugation for high performance liquid chromatography analysis. Several critical parameters affecting the extraction performance including the composition and consumption of switchable deep eutectic solvent, the type and amount of acid, salt amount and extraction time were investigated and optimized. Moreover, the structures of the deep eutectic solvent and the recovered hydrophobic layer were both characterized using Fourier transform infrared spectroscopy, further demonstrating the switching mechanism of the extractant during the extraction process. Under the optimal conditions, enrichment factors of diterpenoid quinones ranged from 59 to 274. Good linearities (r≥0.9963), low detection limits (0.5-0.7 ng/mL), satisfactory precisions (relative standard deviations 0.5%-8.6%) and accuracies (recoveries 94.6%-104.6%) were also obtained. Comparing the proposed switchable deep eutectic solvent-based liquid-phase microextraction with other published methods, the characteristics of the procedure were summarized. The developed method was successfully applied for the preconcentration of four liposoluble diterpenoid quinones from a traditional Chinese herbal medicine of Salvia Miltiorrhiza.

Reversed lipid micellar hollow-fiber liquid-phase microextraction of rotigotine in rat plasma.

A hollow fiber liquid phase microextraction (HF-LPME) based on a reversed lipid micelle as the extraction phase was proposed and combined with high performance liquid chromatography (HPLC) for the determination of rotigotine in biological matrix. In the proposed procedure, pieces of hollow fibers were fastened on a magnetic stir bar using a thread to provide better precision. Rotigotine was extracted from 5 mL of diluted plasma sample phase with pH 6 into reversed lipid micelle (5 mmol/L of dipalmitoyl phosphatidyl choline in n-octanol/water) impregnated in both the wall pores and the lumen of the hollow fiber. After the extraction at 900 rpm and room temperature for 30 min, the acceptor phase of reversed lipid micelle was collected for HPLC analysis. Various parameters affecting the extraction efficiency, such as type of surfactant and organic solvent, surfactant concentration, sample phase pH, salt amount, extraction time, stirring rate, and dilution factor of the plasma sample, were investigated and optimized. Furthermore, the formed reversed lipid micelle was characterized by fluorescence method. Under the optimal conditions, the linear range of rotigotine was between 2 ng/mL and 100 ng/mL with determination coefficient (r2) ≥ 0.9913. It is shown from results of method validation that the satisfactory accuracy (the relative errors between -8.5% and 3.3%), precision (the relative standard deviations from 3.8% to 8.9%), stability and matrix effect were obtained. The enrichment factor (EF) of the reversed lipid micelle-based HF-LPME for rotigotine reached 126. And the feasibility of the proposed method was confirmed by the application to the pharmacokinetic study of rotigotine in rat plasma.

Comparison of three-phase hollow fiber liquid-phase microextraction based on reverse micelle with conventional two-phase hollow fiber liquid-phase microextraction and their applications for analysis of cinnamic acids in traditional Chinese medicines.

A novel three-phase hollow fiber liquid-phase microextraction was developed based on reverse micelle as extraction solvent and acceptor phase, and compared with conventional two-phase hollow fiber liquid-phase microextraction. Both procedures were used in the extraction and concentration of four cinnamic acids (caffeic acid, p-hydroxycinnamic acid, ferulic acid, and cinnamic acid) in traditional Chinese medicines prior to high-performance liquid chromatography analysis. Parameters affecting the two procedures were investigated and optimized to obtain the optimum enrichment factors. The mechanism of the developed procedure was explored and elucidated by comparison with conventional two-phase hollow fiber liquid-phase microextraction. Under the optimized conditions, the analytes' enrichment factors were between 50 and 118 for the proposed procedure, and 31-96 for conventional two-phase mode. Satisfactory linear ranges (r2  ≥ 0.99), detection limits (0.1-0.6 ng/mL), precisions (<9.2%), and accuracies (recoveries: 80-123.1%) were observed for the two procedures. The results showed that the enrichment capacity of the proposed procedure for the cinnamic acids is better than that of conventional two-phase procedure, and both are eco-friendly, simple, and effective for the enrichment and detection of cinnamic acids in traditional Chinese medicines.

Ballpoint connector-protected salt-oil-salt liquid phase microextraction for concentration and enrichment of trace anthraquinone compounds in rhubarb.

This study proposed a new ballpoint connector-protected salt-oil-salt liquid phase microextraction for extraction and enrichment of trace rhein and chrysophanol in rhubarb prior to determination of the analytes by high performance liquid chromatography. In this study, a handy ballpoint connector (between ballpoint tip and ink chamber) was used as extraction device, in which its cavity was filled with n-octanol, and the bare n-octanol in its two opening ends was covered with a thin layer of sodium chloride film. The design subtly assembled salt film onto ballpoint connector for extraction and enrichment, which greatly improved the enrichment factors of the target analytes. Moreover, the novel procedure and its extraction mechanism were described and analyzed, and several crucial parameters reflecting the extraction effect were investigated and optimized. Under optimum conditions, high enrichment factors (247 and 127), good linearities with r ≥ 0.9998, limits of detection (0.6-1.1 ng/mL), relative standard deviations of intra- and interday (2.2-8.8% and 4.3-8.9%), and average recoveries (97.6-98.1%), were obtained, respectively. The proposed method can not only eliminate the negative effects from viscosity and ion strength at high salt concentration of sample phase, but also make salting-out effect be focused on small area so as to maximize the extraction effect.

Three-phase hollow-fiber liquid-phase microextraction based on deep eutectic solvent as acceptor phase for extraction and preconcentration of main active compounds in a traditional Chinese medicinal formula.

A three-phase hollow-fiber liquid-phase microextraction based on deep eutectic solvent as acceptor phase was developed and coupled with high-performance capillary electrophoresis for the simultaneous extraction, enrichment, and determination of main active compounds (hesperidin, honokiol, shikonin, magnolol, emodin, and ß,ß'-dimethylacrylshikonin) in a traditional Chinese medicinal formula. In this procedure, two hollow fibers, impregnated with n-heptanol/n-nonanol (7:3, v/v) mixture in wall pores as the extraction phase and a combination (9:1, v/v) of methyltrioctylammonium chloride/glycerol (1:3, n/n) and methanol in lumen as the acceptor phase, were immersed in the aqueous sample phase. The target analytes in the sample solution were first extracted through the organic phase, and further back-extracted to the acceptor phase during the stirring process. Important extraction parameters such as types and composition of extraction solvent and deep eutectic solvent, sample phase pH, stirring rate, and extraction time were investigated and optimized. Under the optimal conditions, detection limits were 0.3-0.8 ng/mL with enrichment factors of 6-114 for the analytes and linearities of 0.001-13 µg/mL (r2 ≥ 0.9901). The developed method was successfully applied to the simultaneous extraction and concentration of the main active compounds in a formula of Zi-Cao-Cheng-Qi decoction with the major advantages of convenience, effectiveness, and environmentally friendliness.

Sodium dodecyl sulfate sensitized switchable solvent liquid-phase microextraction for the preconcentration of protoberberine alkaloids in Rhizoma coptidis.

A sodium dodecyl sulfate sensitized switchable solvent liquid-phase microextraction method was developed and applied to the preconcentration of active alkaloids in Rhizoma coptidis followed by high performance liquid chromatography determination. Before extraction, nonionic triethylamine was converted to its cationic form in the presence of carbon dioxide. Then, the ionic solvent carrying target analytes was once more reverted to its nonionic form by adding sodium hydroxide, as well as phase separation and analytes enrichment were realized simultaneously. Several parameters affecting the approach, such as concentration of sodium dodecyl sulfate, extraction solvent volume, sodium hydroxide concentration, sample phase pH, injection solvent type, and extraction time, were investigated and optimized. The possible microextraction mechanism of double micelle supramolecular inclusion was explored. Under the optimum conditions, the enrichment factors of four protoberberine alkaloids were from 101.8 to 152.0. The linear ranges (with r2  ≥ 0.990) were 0.032-4.23, 0.031-4.33, 0.0026-10.04, and 0.0013-4.13 µg/mL for epiberberine, coptisine, palmatine, and berberine, respectively. The detection limits were in the range of 0.16-0.32 ng/mL. Satisfactory accuracies (recoveries 98.8-104.6%) and precisions (RSDs 1.9-10.9%) were also obtained. The results showed that the approach is rapid, effective, eco-friendly, and easy-to-handle for the enrichment and detection of active alkaloids in Rhizoma coptidis.