hua Xiao

Application of ionic liquids in the microwave-assisted extraction of polyphenolic compounds from medicinal plants.

Ionic liquids (ILs) solutions as solvents were successfully applied in the microwave-assisted extraction (MAE) of polyphenolic compounds from medicinal plants. ILs, its concentration and MAE conditions were investigated in order to extract polyphenolic compounds effectively from Psidium guajava Linn. (P. guajava) leaves and Smilax china (S. china) tubers. The results obtained indicated that the anions and cations of ILs had influences on the extraction of polyphenolic compounds as well as the ILs with electron-rich aromatic pi-system enhanced extraction ability. Under the optimized conditions, the extraction yields of the polyphenolic compounds were in the range of 79.5-93.8% with one-step extraction, and meanwhile the recoveries were in the range of 85.2-103% with relative standard deviations (R.S.D.s) lower than 5.6%. Compared to conventional extraction procedures, the results suggested that the proposed method was effective and alternative for the extraction of polyphenolic compounds from medicinal plants. In addition, the extraction mechanisms and the structures of samples before and after extraction were also investigated. ILs solutions as green solvents in the MAE of polyphenolic compounds from medicinal plant samples showed a great promising prospect.

Study of vacuum microwave-assisted extraction of polyphenolic compounds and pigment from Chinese herbs

Vacuum microwave-assisted extraction (VMAE), in which microwave-assisted extraction (MAE) was performed in vacuum, was specially designed and applied for the extraction of polyphenolic compounds and pigments from Chinese herbs. The extraction conditions including solid/liquid ratio, extraction time, extraction temperature and degree of vacuum were optimized. Subsequently, VMAE, MAE, and conventional heating reflux extraction (HRE) were evaluated with resveratrol and emodin extraction from Rhizma Polygoni Cuspidati, myricetin and quercetin extraction from Myrica rubra leaves, and safflomin A extraction from Flos Carthami. In addition, the different microstructures of those rhizome, leaf, and flower samples were investigated before and after extraction. It was obvious that the extraction yields of resveratrol, myricetin and safflomin A (thermosensitive compounds) with VMAE were higher than that with MAE or HRE by increments of 6.4-9.4% and 7.9-29.5%, respectively. In contrast, there was no obvious difference among the extraction yields for emodin and quercetin (thermo-stable compounds) with VMAE, MAE and HRE, except that the solvent consumption in VMAE was decreased. The results suggest that VMAE is a good alternative for the extraction of polyphenolic compounds and pigments, especially thermosensitive compounds, from Chinese herbs.

Microwave accelerated selective Soxhlet extraction for the determination of organophosphorus and carbamate pesticides in ginseng with gas chromatography/mass spectrometry.

Microwave accelerated selective Soxhlet extraction (MA-SSE), a novel selective extraction technique, was investigated in this study. A Soxhlet extraction system containing a glass filter was designed as an extractor. During the procedure of MA-SSE, both the target analytes and the interfering components were extracted from the sample into the extraction solvent enhanced by microwave irradiation. After the solvent flowed though the sorbent, the interfering components were adsorbed by the sorbent, and the target analytes remaining in the solvent were collected in the extraction bottle. No cleanup or filtration was required after extraction. The efficiency of the MA-SSE approach was demonstrated in the determination of organophosphorus and carbamate pesticide residues in ginseng by gas chromatography/mass spectrometry (GC/MS). Under the optimized conditions, low limits of detection (0.050-0.50 μg/kg) were obtained. The recoveries were in the range of 72.0-110.1% with relative standard deviations less than 7.1%. Because of the effect of microwave irradiation, MA-SSE showed significant advantage compared with other extraction techniques. The sorbent used in this study showed good cleanup ability. The mechanism of MA-SSE was demonstrated to be based on the rupture of the cell walls according to the structural changes of ginseng samples. On the basis of the results, MA-SSE as a simple and effective sample preparation technique for the analysis of pesticide residues in complex matrixes shows great promise.

Isolation of fucoxanthin from edible brown algae by microwave‐assisted extraction coupled with high‐speed countercurrent chromatography

A rapid and efficient method for the separation and purification of fucoxanthin from edible brown algae by microwave-assisted extraction coupled with high-speed countercurrent chromatography was developed. The algae were first extracted using microwave-assisted extraction, then the dried extract was dissolved and directly introduced into the high-speed countercurrent chromatography system with a two-phase solvent system consisting of hexane-ethyl acetate-ethanol-water (5:5:6:4, v/v/v/v). The isolation was done in less than 75 min, and a total of 0.83 mg, 1.09 mg, and 0.20 mg fucoxanthin were obtained from 25.0 g fresh Laminaria japonica Aresch, 1.5 g dry Undaria pinnatifida (Harv) Sur, and 15.0 g dry Sargassum fusiforme (Harv) Setch, respectively. The purity of fucoxanthin determined by HPLC was over 90% and its structure was further identified by LC-ESI-MS and (1) H-NMR.

Study of polyethylene glycol as a green solvent in the microwave-assisted extraction of flavone and coumarin compounds from medicinal plants

In this paper, the application of polyethylene glycol (PEG) aqueous solution as a green solvent in microwave-assisted extraction (MAE) was firstly developed for the extraction of flavone and coumarin compounds from medicinal plants. The PEG solutions were optimized by a mono-factor test, and the other conditions of MAE including the size of sample, liquid/solid ratio, extraction temperature and extraction time were optimized by means of an orthogonal design L(9) (3(4)). Subsequently, PEG-MAE, organic solvent-MAE, and conventional heating reflux extraction (HRE) were evaluated with nevadensin extraction from Lysionotus pauciflorus, aesculin and aesculetin extraction from Cortex fraxini. Furthermore, the mechanism of PEG-MAE was investigated, including microwave-absorptive property and viscosity of PEG solutions, the kinetic mechanism of PEG-MAE and different microstructures of those samples before and after extraction. Under optimized conditions, the extraction yields of nevadensin from L. pauciflorus, aesculin and aesculetin from C. fraxini were 98.7%, 97.7% and 95.9% in a one-step extraction, respectively. The recoveries of nevadensin, aesculin and aesculetin were in the range of 92.0-103% with relative standard derivation lower than 3.6% by the proposed procedure. Compared with organic solvent-MAE and conventional extraction procedures, the proposed methods were effective and alternative for the extraction of flavone and coumarin compounds from medicinal plants. On the basis of the results, PEG solution as a green solvent in the MAE of active compounds from medicinal plants showed a great promising prospect.

Microwave-assisted extraction performed in low temperature and in vacuo for the extraction of labile compounds in food samples

In this study, low temperature vacuum microwave-assisted extraction, which simultaneous performed microwave-assisted extraction (MAE) in low temperature and in vacuo environment, was proposed. The influencing parameters including solid/liquid ratio, extraction temperature, extraction time, degree of vacuum and microwave power were discussed. The predominance of low temperature vacuum microwave-assisted extraction was investigated by comparing the extraction yields of vitamin C, β-carotene, aloin A and astaxanthin in different foods with that in MAE and solvent extraction, and 5.2-243% increments were obtained. On the other hand, the chemical kinetics of vitamin C and aloin A, which composed two different steps including the extraction step of analyte transferred from matrix into solvent and the decomposition step of analyte degraded in the extraction solvent, were proposed. All of the decomposition rates (K(2)) for the selected analyte in low temperature, in vacuo and in nitrogen atmosphere decreased significantly comparing with that in conventional MAE, which are in agreement with that obtained from experiments. Consequently, the present method was successfully applied to extract labile compound from different food samples. These results showed that low temperature and/or in vacuo environment in microwave-assisted extraction system was especially important to prevent the degradation of labile components and have good potential on the extraction of labile compound in foods, pharmaceutical and natural products.

Hybrid Field-Assisted Solid–Liquid–Solid Dispersive Extraction for the Determination of Organochlorine Pesticides in Tobacco with Gas Chromatography

A novel one-step sample preparation technique termed hybrid field-assisted solid-liquid-solid dispersive extraction (HF-SLSDE) was developed in this study. A simple glass system equipped with a condenser was designed as an extraction vessel. The HF-SLSDE technique was a three-phase dispersive extraction approach. Target analytes were extracted from the sample into the extraction solvent enhanced by the hybrid field. Meanwhile, the interfering components were adsorbed by dispersing sorbent. No cleanup step preceded chromatographic analysis. The efficiency of the HF-SLSDE approach was demonstrated in the determination of organochlorine pesticide (OCP) residues in tobacco with a gas chromatography-electron capture detector (GC-ECD). Various operation conditions were studied systematically. Low detection limits (0.3-1.6 μg/kg) and low quantification limits (1.0-4.5 μg/kg) were achieved under the optimized conditions. The recoveries of OCPs ranged from 70.2% to 118.2%, with relative standard deviations of <9.6%, except for the lowest fortification level. Because of the effect of the hybrid field, HF-SLSDE showed significant predominance compared with other extraction techniques. The dispersing sorbent with good cleanup ability used in this study was also found to be a microwave absorption medium, which could heat the nonpolar extraction solvent under microwave irradiation. Different microstructures of tobacco samples before and after extractions demonstrated the mechanism of HF-SLSDE was based on an explosion at the cell level. According to the results, HF-SLSDE was proved to be a simple and effective sample preparation method for the analysis of pesticide residues in solid samples and could potentially be extended to other nonpolar target analytes in a complex matrix.

Evaluation of vacuum microwave-assisted extraction technique for the extraction of antioxidants from plant samples.

In the present work, vacuum microwave-assisted extraction (VMAE) was to perform microwave-assisted extraction in vacuum. Two well-known antioxidants, vitamin C from guava and green pepper, and vitamin E (alpha-tocopherol and gamma-tocopherol) from soybean and tea leaves, which were easy to be oxidized, were chosen as representative target compounds for the evaluation of VMAE. The extraction yields of vitamin C, alpha-tocopherol and gamma-tocopherol in VMAE and those in MAE performed in atmosphere (air-MAE) were compared and the effects of extraction time, extraction temperature and sample matrix were studied. Moreover, the effects of the oxygen and subpressure invacuo were also discussed via performed MAE in N(2) atmosphere (N(2)-MAE). The extraction yields of vitamin C, alpha-tocopherol and gamma-tocopherol in VMAE were higher than that in air-MAE, 35% increments of vitamin C from green pepper, 22% increments of alpha-tocopherol and 47% increments of gamma-tocopherol from tea leaves were obtained, respectively. The comparable increased extraction yields of vitamin C, alpha-tocopherol and gamma-tocopherol in N(2)-MAE to that in air-MAE confirmed that oxygen in system was the crucial factor for the oxidation of vitamin C and vitamin E, VMAE was beneficial for the extraction of these oxygen-sensitive compounds. In addition, the subpressure invacuo in the VMAE system also showed positive affect on the extraction yields. On the basis of preventing oxidation and improving extraction efficiency of target compounds because of less oxygen and subpressure invacuo in the extraction system, VMAE has good potential for the extraction of oxygen-sensitive and thermosensitive compounds from plant samples.

Rapid analysis of ractopamine in pig tissues by dummy-template imprinted solid-phase extraction coupling with surface-enhanced Raman spectroscopy

Ritodrine has similar skeleton structure to ractopamine and it was selected as the dummy-template molecule to synthesize the molecular imprinted polymers (MIPs). The MIPs exhibited better selectivity to ractopamine than to the dummy-template molecule: the imprint factor for ractopamine was 8.9, while 7.6 for ritodrine. The MIPs were used as sorbents in solid-phase extraction for selective enrichment of ractopamine, and some key parameters were optimized. After that, a rapid surface-enhanced Raman spectroscopy method was developed for analysis of ractopamine and isoxuprine in pig tissue samples. Under the optimal conditions, good linearity was achieved in the range of 20.0-200.0 μg/L for ractopamine and isoxsuprine at 842 cm(-1) and 993 cm(-1), respectively. The limits of detection were 3.1-4.3 μg/L, which were lower than the maximum allowed by U. S. Food and Drug Administration. The recoveries of ractopamine and isoxsuprine were 72.4-79.7% and 71.0-78.2% for the spiked pork and pig liver, respectively, while the relative standard deviations ranging from 7.4% to 13.0%. The results suggest that the proposed method is sensitive and selective, and it has good potential on the quantitative analysis of trace amounts of β-agonists in complex samples.

Porous molecularly imprinted monolithic capillary column for on-line extraction coupled to high-performance liquid chromatography for trace analysis of antimicrobials in food samples.

A novel porous molecularly imprinted monolithic capillary column (MIMCC) based on ternary porogen was synthesized by in situ technique with sulfaquinoxaline as the template molecule. The characteristics of the MIMCC were investigated by scanning electron microscopy, infrared spectrum, thermogravimetric analysis and solvent resistance test. The saturated adsorption amount of sulfaquinoxaline on MIMCC was 2.7 times over that on the non-imprinted monolithic capillary column (NIMCC). The MIMCC also exhibited good enrichment ability to its analogs and the enrichment factors were 46-211 for five antimicrobials. High permeability and imprinting factors as well as good stability, reproducibility and long lifetime were obtained. An on-line method based on MIMCC solid-phase microextraction coupled with high-performance liquid chromatography was developed for the determination of trace antimicrobials in complex samples. The good linearity for sulfametoxydiazine, sulamethoxazole and sulfaquinoxaline was 0.05-10 µg/L, the limits of detection (LODs) were 10.0-14.0 ng/L. The linear range for mequindox and quinocetone were 0.10-10.0 µg/L, the LODs were 20.0-27.0 ng/L respectively. The recoveries were 71.0-108.2% with relative standard deviation of 1.6-8.5%, correspondingly. The results showed that MIMCC could effectively enrich antimicrobials from complex matrices. The on-line method based on MIMCC and HPLC was selective, sensitive and convenient for trace determination of antimicrobials in complex samples.