Determination of Myristicin and Linalool in Plants Exposed to Microwave Radiation by High-Performance Liquid Chromatography

The goal of this study was to develop and validate a high-performance liquid chromatography method for the quantification of two essential oil constituents (myristicin and linalool) from extracts of the three aromatic plants exposed to low-intensity microwave radiation. The analysis was performed by high-performance liquid chromatography using a mobile phase consisting of ultrapure water and acetonitrile. The separations were carried out in the following conditions: isocratic conditions for 30 minutes with 100% acetonitrile and then linear gradient conditions from 100% acetonitrile to 25% acetonitrile for 15 minutes. The developed method was validated in terms of linearity, limits of detection, limits of quantification, precision, accuracy, and robustness. The results show that plants react differently under microwave stress and change their essential oil content as a response.     

Determination of acetonitrile and ethanol in water by guided microwave spectroscopy with multivariate calibration

The feasibility of using guided microwave spectroscopy (GMS) utilizing the frequency range 0.25-3.20 GHz, was combined with multivariate calibration for the determination of acetonitrile or ethanol concentration in water. A wide range of different concentrations was used (up to 30% v/v). Partial least squares (PLS) and weighted ridge regression (WRR) was applied to generate a model for prediction, based upon the microwave spectra. A high level of collinearity was observed in both of the sample data sets and this was reduced by background subtraction. The prediction ability for the two types of regression models were found to be comparable with the percentage error of prediction (PEP) being approximately 2.5% for the acetonitrile samples and 1.1% for ethanol samples.     

Microwave-assisted enzyme-catalyzed reactions in various solvent systems

The work describes the accelerated enzymatic digestion of several proteins in various solvent systems under microwave irradiation. The tryptic fragments of the proteins were analyzed by matrix-assisted laser desorption/ionization mass spectrometry. Under the influence of rapid microwave heating, these enzymatic reactions can proceed in a solvent such as chloroform, which, under traditional digestion conditions, renders the enzyme inactive. The digestion efficiencies and sequence coverages were increased when the trypsin digestions occurred in acetonitrile-, methanol- and chloroform-containing solutions that were heated under microwave irradiation for 10 min using a commercial microwave applicator. The percentage of the protein digested under microwave irradiation increased with the relative acetonitrile content, but decreased as the methanol content was increased. These observations suggest that acetonitrile does not deactivate the enzyme during the irradiation period; in contrast, methanol does deactivate it. In all cases, the digestion efficiencies under microwave irradiation exceed those under conventional conditions.     

Determination of Abamectin Residues in Avocados by Microwave-Assisted Extraction and HPLC with Fluorescence Detection

In this article a new analytical method for the confirmation and quantification of abamectin residues in avocados is described. The method allows a fast analysis of abamectin homologues using microwave assisted extraction (MAE), solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with fluorescence (FL) detection using trifluoroacetic anhydride (TFAA) and N-methylimidazole (NMIM) as derivatizing agents. The mobile phase consisted of water, methanol and acetonitrile (5:47.5:47.5 v/v/v) and was pumped at a rate of 1.1 mL min⁻¹ (isocratic elution). Homogenized avocado samples were extracted once with 20 mL acetonitrile:water 4:1 (v/v) in a microwave oven for 26 min at 700 W with a maximum temperature of 80 °C. MAE operational parameters were optimized by means of an experimental design. Extracts were cleaned using C₁₈ SPE cartridges. Average recoveries of the method at four spiked levels (0.005, 0.01, 0.10 and 1.0 mg kg⁻¹) were found to be in the range 90–100% with good precision (RSD < 12%). The limits of detection (LODs) and quantification (LOQs) of the whole method were 0.001 and 0.003 mg kg⁻¹, respectively, which are lower than the maximum residue limit (MRL) established by the Spanish and the European legislation in avocados (0.01 mg kg⁻¹). Several avocado samples previously treated with the pesticide were also analyzed.     

Sonogashira reaction on pyridinium N-heteroarylaminides

The reactivity of N-(5-iodopyridin-2-yl)aminide in a copper-free Sonogashira cross-coupling process is reported. The reaction proceeds on using PdCl₂(PPh₃)₂ and DABCO as the base under microwave irradiation in acetonitrile or water as solvents. The process can also be carried out by traditional heating in acetonitrile on using Pd(AcO)₂/DABCO with Cs₂CO₃.     

Extraction and analysis of avermectines in agricultural soils by microwave assisted extraction and ultra high performance liquid chromatography coupled to tandem mass spectrometry

A method for the analysis of avermectines (abamectine, doramectine and ivermectine) in soils has been developed. The analytes are extracted with acetonitrile/water (90:10) by using microwave assisted extraction. The extract is cleaned-up through solid phase extraction with Oasis HLB cartridges and analyzed by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Separation is obtained in 3 min. Extraction of analytes from the soil, that is the most critical point, has been studied in detail, and the effect of soil composition and aging time on the analytes recovery has been investigated.     

Ultramicro Analysis of Reducing and Non-Reducing Sugars by Liquid Chromatography

Abstract

A post-column detection system for ultramicro amount of sugars has been developed using taurocyamine as the labelling reagent. Less than 10 pmol of reducing sugars were determined by this HPLC system. Non-reducing sugars were detected by the addition of periodate to the reagent.

Modification of the reaction reagent components made this detection system feasible to apply to various methods for separation of carbohydrates using pure water, acetonitrile/water mixtures, borate buffer or aqueous sodium hydroxide as the eluent.     

Separation and purification of steroidal saponins from Paris polyphylla by microwave‐assisted extraction coupled with countercurrent chromatography using evaporative light scattering detection

A method of microwave‐assisted extraction coupled with countercurrent chromatography using evaporative light scattering detection was successfully developed for the separation and purification of steroidal saponins from Paris polyphylla. The main extraction conditions including microwave power, liquid/solid ratio, irradiation time, and extraction temperature were optimized using an orthogonal array design method. A suitable two‐phase solvent system consisting of n‐heptane/n‐butanol/acetonitrile/water (10:19:6:20, v/v/v/v) was employed in the separation and purification of the extracts of P. polyphylla. A total of 7.1 mg polyphyllin VII, 4.3 mg gracillin, 9.2 mg dioscin, and 10.2 mg polyphyllin I were obtained from 1.5 g P. polyphylla in less than 300 min, the purities of which determined by HPLC were 96.7, 97.3, 98.7, and 98.6%, respectively. The identification and characterization of these compounds were performed by LC–ESI‐MS and ¹H NMR spectroscopy. The results demonstrated that the proposed method is feasible, economical and efficient for the extraction, separation and purification of effective compounds from natural products.     

Determination of sulfonamides in swine muscle after salting-out assisted liquid extraction with acetonitrile coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system prior to high-performance liquid chromatography

A salting-out assisted liquid extraction coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system combined with high-performance liquid chromatography with diode-array detection (HPLC–DAD) was developed for the extraction and determination of sulfonamides in solid tissue samples. After the homogenization of the swine muscle with acetonitrile and salt-promoted partitioning, an aliquot of 1 mL of the acetonitrile extract containing a small amount of dichloromethane (250–400 μL) was alkalinized with diethylamine. The clear organic extract obtained by centrifugation was used as a donor phase and then a small amount of water (40–55 μL) could be used as an acceptor phase to back-extract the analytes in the water/acetonitrile/dichloromethane ternary component system. In the back-extraction procedure, after mixing and centrifuging, the sedimented phase would be water and could be withdrawn easily into a microsyringe and directly injected into the HPLC system. Under the optimal conditions, recoveries were determined for swine muscle fortified at 10 ng/g and quantification was achieved by matrix-matched calibration. The calibration curves of five sulfonamides showed linearity with the coefficient of estimation above 0.998. Relative recoveries for the analytes were all from 96.5 to 109.2% with relative standard deviation of 2.7–4.0%. Preconcentration factors ranged from 16.8 to 30.6 for 1 mL of the acetonitrile extract. Limits of detection ranged from 0.2 to 1.0 ng/g.     

Mobile phase effects on retention on a new butylimidazolium-based high-performance liquid chromatographic stationary phase

A new HPLC stationary phase based on n-butylimidazolium bromide has been characterized by a linear solvation energy relationship (LSER) approach in the binary acetonitrile/water mobile phases. The retention properties of the stationary phase were systematically evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phase. The results and further comparisons with conventional reversed phase system confirm that retention properties are similar to phenyl phases in acetonitrile/water mixtures. The results obtained with acetonitrile/water mixtures are also compared with results obtained using methanol/water mixtures.     

Self-generated hierarchically porous titania with high surface area: photocatalytic activity enhancement by macrochannel structure

Various hierarchical porous titania with high surface area over 600 m(2)/g have been synthesized via a spontaneous self-formation process from titanium alkoxides by a water adjusting approach using acetonitrile as reaction medium. The reactivity of metal alkoxides and the water content in acetonitrile medium on the resultant structure have been investigated. The porosities of the products were characterized by SEM, TEM and N(2) adsorption-desorption measurements. The observation on the evolution of porous structure with increasing water content in reaction system is essential for a better understanding of hierarchical porous structure formation over different length scales by this self-formation process. The creation of macro/micropores in photocatalytic titania materials has been found to enhance the photocatalytic activity due to both the action of macrochannels as light harvester and the easy diffusion effect of organic molecules. The present work shows clearly that hierarchically porous titania with the presence of macroporous structure and high surface area can be very efficient photocatalysts, suggesting their potential applications in water treatment as decontamination materials.     

Combination of a modified quick,easy, cheap,efficient, rugged,and safe extraction method with a deep eutectic solvent based microwave‐assisted dispersive liquid–liquid microextraction: Application in extraction and preconcentration of multiclass pesticide residues in tomato samples

In this study, a new two–step extraction procedure based on the combination of a modified quick, easy, cheap, effective, rugged, and safe extraction method with a deep eutectic solvent based microwave‐assisted dispersive liquid–liquid microextraction has been developed for the extraction of multiclass pesticides in tomato samples before their analysis by gas chromatography with flame ionization detection. In this method, initially, an aliquot of tomato is crushed and diluted with deionized water. The mixture is then passed through a filter paper and its residue and aqueous phase are separated. Afterwards, acetonitrile as an extraction/disperser solvent is passed through the filter paper containing the refuse. The analytes remained in the refuse are extracted into the acetonitrile and then the obtained extract is mixed with a deep eutectic solvent. The obtained mixture is injected into the tomato juice and placed in a microwave oven for 15 s. Consequently, a cloudy state is formed and the extractant containing the analytes are sedimented at the bottom of the tube after centrifugation. Finally, 1 μL of the sedimented phase is removed and injected into the separation system. Under the optimum conditions, limits of detection and quantification were in the ranges of 0.42–0.74 and 1.4–2.5 ng/g, respectively.     

亲水作用色谱-四极杆/静电场轨道阱高分辨率质谱快速测定水样中氨基脲

建立了亲水作用色谱-四极杆/静电场轨道阱高分辨质谱快速检测水中氨基脲的方法。水样中加入0.1 mol/ L NaOH 溶液后,以乙腈为提取剂,加入过量 Na2 SO4,使乙腈与水分层,乙腈提取液再经无水 Na2 SO4脱水后,采用亲水作用色谱柱 Amide 色谱柱分离,以0.1%甲酸水溶液及0.1%甲酸乙腈溶液为流动相进行梯度洗脱,四极杆/静电场轨道阱高分辨率质谱电喷雾正离子、选择离子监测模式检测,同位素内标法进行定量分析。在最优实验条件下,氨基脲在0.2~20μg/ L 浓度范围内线性相关系数为0.997,方法的检出限为0.09μg/ L,定量限为0.30μg/ L。以淡水和海水为空白样品,在添加浓度为0.5,1.0和5.0μg/ kg 水平下,氨基脲的加标回收率为82.3%~92.0%,相对标准偏差小于7.6%。本方法适用于环境水样中氨基脲的快速分析。     

Molecular imprinting polymerization by Fenton reaction

The aim of this study is the preparation of molecularly imprinted polymers by employing a redox pair as initiator system. Bulk molecularly imprinted polymers were synthesized by using Fenton reagents as initiator system. Theophylline, methacrylic acid, and ethylene glycol dimethacrylate were employed as model template, functional monomer, and crosslinking agent, respectively. Conventional imprinted polymers were also prepared by using 2,2′-azoisobutyronitrile in order to evaluate the efficiency of the proposed initiator system. Redox molecularly imprinted polymers and conventional molecularly imprinted polymers were characterized by water uptake measurement, while the imprinting effect of synthesized polymers were evaluated by performing binding experiments in organic (acetonitrile) and in water (buffered water solution at pH = 7.4) media.     

液相色谱-质谱联用法测定牛奶中14种青霉素及相应青霉噻唑酸残留量

利用超高效液相色谱-串联质谱法(UPLC-MS/MS)同时测定牛奶中的7种青霉素类抗生素以及7种相应的青霉噻唑酸。样品经乙腈沉淀蛋白,上清液N2吹干后,用水溶解,加入正己烷萃取除去脂肪;提取液经ACQUITY UPLCBEH C18柱分离,乙腈-乙酸铵+甲酸水溶液洗脱。14种物质峰分离良好,定量限范围在5～20μg/kg。在10～50ng/mL质量浓度范围内线性良好,相关系数均大于等于0.999,牛奶中的加标回收率在90%～98%。     

Analysis of underivatized amino acid mixtures using high performance liquid chromatography/dual oscillating nebulizer atmospheric pressure microwave induced plasma ionization-mass spectrometry

A dual oscillating capillary nebulizer (OCN) in conjunction with an atmospheric pressure microwave induced plasma ionization (AP-MIPI) source was applied to the analysis of underivatized amino acid mixtures. It was found that, compared to the single OCN, the dual OCN enhanced the sensitivity of detection several fold. Enhanced sensitivity was compound dependent. For small molecules, such as amino acids, it was 2-5 times more sensitive, while for larger molecules such as peptides it was more than an order of magnitude. The increase in sensitivity was attributed to the enhanced nebulization of the new torch. By using water/ acetonitrile containing 0.1% nonafluoropentanoic acid as the high performance liquid chromatography (HPLC) mobile phase and a C18 column, all common amino acids were separated and detected. A comparison between the results obtained using microwave induced plasma, atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI) at flow rates compatible with micro LC (10-100 microL/min) showed a higher sensitivity of detection with the AP-MIPI technique for the analysis of underivatized amino acids.     

Study on Preferential Solvation of Water by Electrochemical Method

The preferential solvation of water plays an important role in ferrocene research which is a subject of current interest. Voltammetric investigations were carried out for Au electrode in acetonitrile/water, showing preferential solvation of water. In our work, the preferential solvation of water in acetonitrile/water was studied by electrochemical methods including cyclic volitammetry, electrochemical impedance spectra and double‐step chronoamperometry. Ferrocenemethanol (FcCH₂OH) molecules as a solute spontaneously adsorb on the electrode surface in anhydrous acetonitrile, resulting from acetonitrile molecules tend to form an acetonitrile solvent layer on the surface of the electrode and acetonitrile solvent layer has a lower energy barrier than the aqueous solvent layer, which has been obtained by modeling solvation. The solvent strongly influences electrochemical behavior of solute. Once there is an amount of water in acetonitrile solvent, FcCH₂OH that adsorbed on the electrode surface desorb. This is because water preferentially solvate with FcCH₂OH in term of intermolecular forces between solvent and solute. Moreover, hydrogen bond between water molecules and FcCH₂OH molecules is stronger than dipole‐dipole interaction between acetonitrile molecules and FcCH₂OH molecules in solvation effect. Through electrochemical behavior of FcCH₂OH changing, preferential solvation of water is analyzed by electrochemical methods.     

First separation of four aromatic acids and two analogues with similar structures and polarities from Clematis akebioides by high‐speed counter‐current chromatography

In this paper, we report an efficient method by high‐speed counter‐current chromatography for the first separation of four aromatic acids and two analogs with similar structures and polarities from Clematis akebioides. First, the ethyl acetate extract was treated by silica gel column chromatography to enrich the target compounds. And then the fraction with target compounds were purified by high‐speed counter‐counter chromatography using a two‐phase solvent system consisting of chloroform/acetonitrile/water (10:6:4, v/v). The results showed high‐speed counter‐current chromatography could be a powerful technology for the separation of compounds with similar structures and polarities. Besides, it was found acetonitrile could be a good methanol substitute when a chloroform/methanol/water system could not provide a good separation factor. This study provides a reference for the separation of compounds from Clematis akebioides.     

A Facile Synthesis of New L‐Proline‐Based Trifluoromethyl Oxazole Derivatives Using Microwave Irradiation and Conventional Method

Cyclization reaction of l ‐proline with trifluoroacetimidoyl chlorides has been developed as an efficient strategy for the synthesis of trifluoromethyl oxazole derivatives by two methods: (a) in the presence of K₂CO₃ as a base in acetonitrile at room temperature and (b) in the presence of K₂CO₃ as a base in acetonitrile using microwave irradiation, in one pot reaction. The microwave irradiation has been found to be the most efficient method. High yields and short reaction times were obtained for both electron‐releasing and electron‐withdrawing substituted N‐aryltrifluoroacetimidoyl chloride derivatives by microwave irradiation.     

Contact conductivity detection of polymerase chain reaction products analyzed by reverse-phase ion pair microcapillary electrochromatography

We describe the development of an integrated microelectrophoretic system consisting of a contact conductivity detector mounted on-chip for monitoring the separation of double-stranded (ds) DNA fragments produced via the polymerase chain reaction (PCR) using microcapillary electrochromatography as the separation mode. The separation was carried out in a polymer-based microfluidic device, hot-embossed into poly(methylmethacrylate) (PMMA), whose walls were functionalized to produce a C(18)-terminated surface to act as the stationary phase (open channel format). The carrier electrolyte contained the ion-pairing agent, triethylammonium acetate (TEAA) to allow the separation to be carried out using reverse-phase ion-pair capillary electrochromatography (RP-IPCEC). The microelectrophoretic separations were investigated utilizing various solvent strengths (acetonitrile/water) with 25 mM TEAA to observe the effects on the separation efficiency as well as the chromatographic development time and detector performance. The field strength significantly affected the quality of the separation, with no separation observed at 333 V/cm for a low mass dsDNA sizing ladder, but baseline separation achieved using a field strength of 67 V/cm. It was observed that the solvent strength affected the retention behavior of the polyanionic molecules as well as the electroosmotic mobility. Higher acetonitrile compositions in the run buffer resulted in reduced plate numbers, which produced lower chromatographic resolution. The use of conductivity detection allowed mass detection sensitivities in the range of 10(-21) mol with a separation efficiency of 10(4) plates and the performance of the detector independent of the acetonitrile content used in the carrier electrolyte.