Volume Of Dichloromethane Research Articles

Ultrasound-assisted dispersive liquid–liquid microextraction combined with ion mobility spectrometry for the simultaneous preconcentration and determination of dimethoate and chlorpyrifos in fruit, vegetable, and water samples

A rapid, sensitive, and reliable method based on ultrasound- assisted dispersive liquid–liquid microextraction followed by ion mobility spectrometry analysis (UA-DLLME-IMS) is reported for the preconcentration and determination of chlorpyrifos and dimethoate in food and water. The sample pH, volume of dichloromethane (extraction solvent), sonication, and centrifuge time, salt effect and sample volume were individually optimized. Under the optimum conditions, the calibration curves were linear from 5 to 200 µg L−1 and 3 to 280 µg L−1. Limits of detection (LOD) of 1.3 and 0.8 µg L−1 were obtained for chlorpyrifos and dimethoate, respectively. The relative standard deviations at 20 μg L−1 (n = 5) for intra- and inter-day precision were 2.8% and 3.9% for chlorpyrifos and 4.1% and 4.6% for dimethoate, respectively. The procedure was validated for the determination of chlorpyrifos and dimethoate in food and water samples.

Pulmonary Delivery of Docetaxel and Celecoxib by PLGA Porous Microparticles for Their Synergistic Effects Against Lung Cancer.

Using a combination of chemotherapeutic agents with novel drug delivery platforms to enhance the anticancer efficacy of the drug and minimizing the side effects, is imperative to lung cancer treatments. The aim of the present study was to develop, characterize, and optimize porous poly (D, L-lactic-co-glycolic acid) (PLGA) microparticles for simultaneous delivery of docetaxel (DTX) and celecoxib (CXB) through the pulmonary route for lung cancer. Drug-loaded porous microparticles were prepared by an emulsion solvent evaporation method. The impact of various processing and formulation variables including PLGA amount, dichloromethane volume, homogenization speed, polyvinyl alcohol volume, and concentration, was assessed based on entrapment efficiency, mean release time, particle size, mass median aerodynamic diameter, fine particle fraction, and geometric standard deviation using a twolevel factorial design. An optimized formulation was prepared and evaluated in terms of size and morphology using a scanning electron microscope. FTIR, DSC, and XRD analyses confirmed drug entrapment and revealed no drug-polymer chemical interaction. Cytotoxicity of DTX along with CXB against A549 cells was significantly enhanced compared to DTX and CXB alone and the combination of DTX and CXB showed the greatest synergistic effect at a 1/500 ratio. In conclusion, the results of the present study suggest that encapsulation of DTX and CXB in porous PLGA microspheres with desirable features is feasible and their pulmonary co-administration would be a promising strategy for the effective and less toxic treatment of various lung cancers.

Minocycline Hydrochloride Controlled-release Microsphere Preparation Process Optimization Based on the Robust Design Method.

The objective of the present study is to establish a robust preparation method that could steadily produce minocycline hydrochloride (MCH) microspheres regardless of used polymer types. Taguchi's Robust Experimental Design methodology was employed to optimize the process parameters for MCH-loaded poly(D,L-lactide-co-glycolide) (PLGA) microspheres. In the experimental design, seven controllable factors, i.e., preparation method, pH of the aqueous phase, volume of the aqueous phase, volume of dichloromethane, rotation speed, temperature, and amount of polyvinyl alcohol, were considered for the optimization of process parameters. PLGA types with different lactide/glycolide ratios were considered the uncontrollable (noise) factor. Based on the L18 orthogonal array, 18 experimental runs were conducted for each type of PLGA. The encapsulation efficiency (EE) and in vitro release rate were evaluated for all the prepared formulations. Regardless of the PLGA type with different lactic/glycolic acid ratios, microspheres prepared via the solid-in-oil-in-water (S/O/W) method, showed a much higher EE and faster drug release than the microspheres prepared via the co-solvent method. Preparation methods, pH of the aqueous phase, and volume of the aqueous phase were the most influencing parameters on the EE. The confirmation experiment results indicated that the signal-to-noise ratio increased by 5.76 db from that of an initial condition. The release of minocycline was fastest with the PLGA (50:50) microspheres, followed by PLGA (75:25) and PLGA (85:15). Although the interaction between the selected factors in the evaluation was ignored, the orthogonal array design of the experiment based on Taguchi's robust experimental design methodology was sufficient to optimize the process parameters for the PLGA microspheres of MCH. The S/O/W was the main factor affecting the EE. Microspheres prepared via the S/O/W method exhibited a higher EE and faster drug release than the microspheres prepared via co-solvent method. The pH and volume of the aqueous phase were also effective parameters on the EE. A robust experimental design has been successfully applied to the optimization of the process parameters for microsphere preparation.

Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation

Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.

Preparation and evaluation of PLGA microparticles as carrier for the pulmonary delivery of rhIL-2 : I. Effects of some formulation parameters on microparticle characteristics

In this study, recombinant human interleukin-2 (rhIL-2) containing poly(lactic-co-glycolic acid) (PLGA) microparticles were prepared for pulmonary administration by modified w/o/w double emulsion solvent extraction method and the effects of various formulation parameters on the physicochemical properties of the microparticles were investigated. Microparticles in suitable size for pulmonary administration (4.02 µm) were obtained by increasing dichloromethane volume used in the organic phase. Also, a very high encapsulation efficiency (99.22%) value could be reached in these microparticles. In the sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis, rhIL-2 extracted from microparticles having a similar band with native rhIL-2 showed that the protein was not affected by the encapsulation process. The release curves of microparticles exhibited a biphasic fashion, characterized by a fast release phase at initial 1 day, followed by a slower one on the remaining days. Bioactivity investigations using T cells show that rhIL-2 encapsulated in PLGA microparticles retain their biological activity.

Development and validation of analytical methods for ethyl carbamate in various fermented foods

The aim of this work was to develop and validate analytical methods for ethyl carbamate (EC) in various food matrices. Column chromatography was used for the analysis of EC in kimchi, a fermented soybean paste (doenjang), a fermented fish product (jeotgal), yoghurt, bread, and cheese. To remove the fat in the bread and cheese, a Florisil cartridge was selected. The volume of dichloromethane in the chromatography column was optimised to 60mL for the kimchi, cheese, and fermented soybean paste. For the bread, jeotgal, and yoghurt, the best recovery rate was found by using 100mL of dichloromethane. For the accurate analysis of EC in the vinegar, 150mL of dichloromethane and a neutralisation process (pH=8.0) were required. In the standard curve of EC, satisfactory linearity (R2=0.998) was shown. The limit of quantification (LOQ) was 10ng/mL and the recovery rates ranged from 76.9% to 118.1%. Intra- and inter-assay precision ranged from 3.5% to 34.2% and 3.8% to 41.9%, respectively.

KINETIC STUDY OF S-ALKYLATION OF 2-MERCAPTOBENZIMIDAZOLE CATALYZED BY TETRABUTYLAMMONIUM BROMIDE

The S-alkylation of 2-mercaptobenzimidazole (MBI) by α-bromo-m-xylene (RBr) under phase transfer catalytic reaction condition was successfully carried out in an aqueous solution of KOH/organic solvent two-phase medium. No product was obtained from N-alkylation during or after the reaction period by using a limited quantity of α-bromo-m-xylene. The reaction is greatly enhanced by adding a small amount of tetrabutylammonium bromide (TBAB) and/or potassium hydroxide. Based on the experimental evidence, a rational reaction mechanism is proposed. A kinetic model is derived, from which a pseudo steady-state hypothesis (PSSH) is applied to the reaction system. The kinetic behaviors and the characteristics of the reaction are sufficiently described by the pseudo first-order rate law. The effects of the reaction conditions, including agitation speed, amount of TBAB catalyst, amount of KOH, quaternary ammonium salts, volume of water, volume of dichloromethane, amount of 2-mercaptobenzimidazole, amount of α-bromo-m-xylene, inorganic salts, organic solvents, and temperature on the conversion of the reactant and the apparent rate constants (kapp) were investigated in detailed. Rational explanations are provided for the observed phenomena from experimental results.

Kinetic study of S-alkylation of 2-mercaptobenzimidazole by allyl bromide in the presence of potassium hydroxide

The S-alkylation (substitution on sulfur atom) of 2-mercaptobenzimidazole (MBI or ArSH) by allyl bromide (RBr) was successfully carried out in an aqueous solution of KOH/organic solvent two-phase medium. The reaction, which may take place either in the organic phase or on the interface, is greatly enhanced in the presence of KOH without the aid of quaternary salts as the catalyst to promote the reaction. No product was obtained from N-alkylation (substitution on nitrogen atom) during or after the reaction period by using a limited amount of allyl bromide (RBr) relative to that of MBI. Based on the experimental evidence, the kinetic behaviors and the characteristics of the reaction are sufficiently described by the pseudo-first-order rate law. The effects of the reaction conditions, including the agitation speed, the amount of KOH, volume of water, volume of dichloromethane, amount of allyl bromide, amount of 2-mercaptobenzimidazole, organic solvents and temperature on the conversion of allyl bromide and the apparent rate constants ( k app) were investigated in detail. Peculiar result is obtained in studying the effect of the volume of water on the conversion (or the reaction rate) in this work. Rational explanations are provided for the observed phenomena from experimental results.

Ultrasound-assisted solvent extraction of total polycyclic aromatic hydrocarbons from mussels followed by spectrofluorimetric determination

An ultrasound-assisted solvent extraction procedure has been optimised to speed up total polycyclic aromatic hydrocarbons (T-PAHs) extraction from mussel soft tissue. The T-PAHs releases have been evaluated by spectrofluorimetry (excitation and fluorescence emission wavelengths of 300 and 382 nm, respectively, and using chrysene as calibrant). Variables such as sonication time, ultrasound frequency, n-hexane volume, dichloromethane volume, number of repeated extractions with n-hexane and number of repeated extraction with dichloromethane were simultaneously studied by applying a Plackett–Burman design (PBD) approach. Results showed that ultrasound frequency and n-hexane and dichloromethane volumes were statistically significant variables (confidence interval of 95%). These last two variables were finally optimised by using central composite designs (CCD), yielding optimum n-hexane and dichloromethane volumes of 2.5 and 6.5 ml, respectively. The lowest T-PAHs releasing at high ultrasound frequency (35 kHz) led to choice the lowest ultrasound frequency (17 kHz) to perform the extraction. Variables such as sonication time and number of repeated extraction with n-hexane or dichloromethane were statistically non-significant and they were fixed at 10 min and the extraction with n-hexane and dichloromethane were performed once. The limit of detection was 0.021 μg g −1 (referred to dried mass), the repeatability of the overall method was 4.7% ( n = 9) and the analytical recoveries were between 98 and 105%. The proposed method was finally applied to 16 mussel samples ( Mytilus galloprovincialis) from Ría de Arousa estuary (Galicia, northwest Spain).

Separation of organotin compounds by using the difference in partition behaviour between hexane and methanolic buffer solution. Part 1. Determination of butyltin compounds in textiles by graphite furnace atomic-absorption spectrophotometry

A method for determining tributyltin compounds (TBTs) and dibutyltin compounds (DBTs) in textiles has been studied by graphite furnace atomic-absorption spectrophotometry. They are successfully extracted from textiles with methanol containing 0.05% of hydrogen chloride. Their partition between hexane and a methanolic buffer solution (pH 8.5) was studied by varying the methanol concentration of the aqueous buffer phase. Only TBTs can be extracted with hexane from a methanolic buffer solution consisting of 40 ml of methanol and 30 ml of buffer solution. TBTs are absorbed on an alumina column and eluted with a small volume of dichloromethane. DBTs remaining in the aqueous phase are extracted with dichloromethane as a complex with 4-(2-pyridylazo)resorcinol. After evaporation of the dichloromethane, the residue is heated with concentrated nitric acid and its tin concentration is determined by atomic-absorption spectrophotometry.