Development of a fritless packed column for capillary electrochromatography-mass spectrometry

A novel procedure was developed for the fabrication of a fritless packed column for the coupling of capillary electrochromatography (CEC) to mass spectrometry (MS). The process involved the formation of internal tapers on two separate columns. Once the internal tapers are formed and the columns are packed, the untapered ends of each column were joined together by a commercially available connector. Several advantages of the fritless columns are described. First, the design used here eventually eliminates the need for any frits thus reducing the possibility of bubble formation seen with fritted packed columns. In addition, this is the first report in which the internal tapers are formed at both the inlet and outlet column ends making the fritless CEC-MS column more robust compared to only one report with externally tapered counterparts. Second, a comparison of internally tapered single frit packed CEC-MS (previously developed in our laboratory) column versus fritless CEC-MS column reported here shows that the latter provides better efficiency, suggesting no dead volume with equally good sensitivity and chiral resolution of (±)-aminoglutethimide. The fritless column procedure is universal and was used to prepare a series of columns with a variety of commercially available packing material (mixed mode strong cation exchange, SCX; mixed mode strong anion exchange, SAX; C-18) for the separation and MS detection of short chain non-chromophoric polar amines, long chain nonchromophic anionic surfactant as well as oligomers of non-chromophoric non-ionic surfactants, respectively. The fritless columns showed good intra-day repeatability and inter-day reproducibility of retention times, chiral and achiral resolutions and peak areas. Very satisfactory column-to-column and operator-to-operator reproducibility was demonstrated.     

Synthesis of silver nanoparticles using root extract of Duchesnea indica and assessment of its biological activities

Treatment of microbial infections and inflammatory conditions have many challenges in terms of efficacy and safety issues. Novel approaches such as nanoparticles based drug delivery system have shown promising results to solve some of these problems. The aim of this study was to exploit the efficacy of the synthesized silver nanoparticles. In this study, silver nanoparticles (AgNPs) were biosynthesized using root extract (aqueous) of Duchesnea indica. They were characterized using different techniques such as, ultraviolet–visible (UV–Vis) spectrophotometry, transmission and scanning electron microscopy (TEM and SEM), X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), fourier-transform infrared spectroscopy (FTIR) and zetasizer. The UV–Vis spectra gave a characteristic peak at 423 nm; XRD confirmed its crystalline structure; FTIR confirmed the involvement of phytochemicals in their capping and reduction; TEM images confirmed their spherical shape with average width of 20.49 nm and average area of 319.25 nm². Various biological activities were performed on these NPs, such as antimicrobial, anti-inflammatory, analgesic and muscle relaxant, which showed significant results as follow. Among bacterial strains, Salmonella typhi (MIC: 0.01 mg/ml) and Escherichia coli (MIC: 0.01 mg/ml), while among that of fungal Microsporum canis (MIC: 0.53 mg/ml) and Alternaria alternata (MIC: 0.51 mg/ml) were most susceptible. The AgNPs showed maximum anti-inflammatory activity (46.15 and 56.85%) at 20 mg/kg after 3 and 5 h of drug administration, comparable to that of standard. In-vivo model exhibited concentration dependent inhibition of both COX-2 and 5-LOX enzymes. Similarly, it exhibited maximum analgesic activity (54.24%) at 20 mg/kg dose after 60 min. of pain induction. Furthermore, they depicted maximum muscle relaxation (P < 0.01) after 60 and 90 min of drug administration. Above results suggest that these AgNPs can be studied further for the development of more effective and safe formulations.     

Multivariate approach for the enantioselective analysis in MEKC‐MS: II. Optimization of 1,1′‐binaphthyl‐2,2′‐diamine in positive ion mode

Enantiomeric separation and detection of 1,1′‐binaphthyl‐2,2′‐diamine (BNA) has been successfully optimized by MEKC‐ESI‐MS using a polymeric surfactant polysodium N‐undecenoxycarbonyl‐L‐leucinate (poly‐L‐SUCL) as a pseudostationary phase. In the first step, MEKC conditions were optimized by a five‐factor three‐level central composite design (CCD) of experiment. All five MEKC factors (buffer pH, percentage of ACN in the running buffer, concentration of surfactant, concentration of ammonium acetate (NH₄OAc), and voltage) were found significant to the responses (measured as the chiral resolution and analysis time). The interactions between MEKC factors were further evaluated using a quadratic model equation which allowed the generation of 3‐D response surface image to reach the optimum conditions. To obtain the best S/N, sheath liquid composition and spray chamber parameters were successfully optimized using the same strategy. Baseline enantiomeric resolution in less than 20 min and optimum MS signal of BNA enantiomers (S/N = 45 at 0.4 mg/mL) were ultimately achieved at the optimized conditions. The adequacy of the model was validated by experimental runs at the optimal predicted conditions. The predicted results were found to be in good agreement with the experimental data.     

Chiral separations in microemulsion electrokinetic chromatography. Use of micelle polymers and microemulsion polymers

In this study, microemulsions of the chiral surfactant polysodium N-undecenoyl-D-valinate (poly-D-SUV) was utilized for enantiomeric separation by investigating two approaches using polymeric chiral surfactant in microemulsion electrokinetic chromatography (MEEKC). In the first approach, poly-D-SUV was used as an emulsifier surfactant along with 1-butanol and n-heptane. Enantioseparation of anionic or partially anionic binaphthyl derivatives, anionic barbiturates, and cationic paveroline derivatives were achieved by varying the mass fraction of 1-butanol, n-heptane and poly-D-SUV. For anionic or partially anionic analytes, relatively lower mass fractions of n-heptane, and poly-D-SUV were found to give optimum chiral separations as compared to that for cationic solutes. In the second approach, the chiral microemulsion polymer was prepared by polymerizing mixtures of 3.50% (w/w) of sodium N-undecenoyl-D-valinate (D-SUV) and 0.82% (w/w) of n-heptane (core phase) at varying concentration of 1-butanol. After polymerization, the n-heptane and 1-butanol were removed to yield solvent free microemulsion polymers (MPs) which were then utilized for the separation of anionic binaphthyl derivatives and anionic barbiturates. When MPs of D-SUV were utilized for chiral separation, 1.00% (w/w) 1-butanol and 3.50% (w/w) 1-butanol was optimum for enantioseparation of (+/-)-BNP and (+/-)-BOH, respectively. On the other hand, for anionic (+/-)-barbiturates very low concentration of butanol (0.25%, w/w) provided optimum resolution. Compared with micellar electrokinetic chromatography (MEKC), the use of micelle polymers or microemulsion polymers in MEEKC showed dramatic enhancement for resolution of (+/-)-BNP, while this enhancement was less dramatic for other binaphthyls [(+/-)-BOH, (+/-)-BNA] as well as for (+/-)-barbiturates and (+/-)-paveroline derivatives. However, higher separation efficiency of the enantiomers was always observed with MEEKC than in MEKC.     

Synthesis of poly(2‐hydroxyethyl methacrylate)‐based molecularly imprinted polymer nanoparticles containing timolol maleate: morphological,thermal, and drug release along with cell biocompatibility studies

This work was aimed to synthesize and characterize poly(2‐hydroxyethyl methacrylate) [poly (HEMA)]‐based molecularly imprinted polymer nanoparticles (MIP NPs) containing timolol maleate (TM) via precipitation polymerization. The molecular structures of the MIP and non‐imprinted polymer (NIP) NPs were compared by means of Fourier transform infrared spectroscopy. The morphological observations by using scanning electron microscopy and transmission electron microscopy confirmed the formation of MIP NPs as small as 128 nm in average diameter with appropriate synthesis conditions. Thermal behaviors of the samples were also studied by the use of thermogravimetric analysis and differential scanning calorimetry. By considering a series of key factors such as monomer : template ratio, cross‐linker type, pH, and temperature, the sample with promising characteristics was found to be that of HEMA : TM ratio of 10:1, 40 mmol of ethylene glycol dimethacrylate as cross‐linker, and polymerization temperature of 60°C in acetonitrile as porogenic solvent. Furthermore, the ultraviolet‐visible (UV‐vis) spectrophotometry results proved a controlled release of TM from the MIP NP samples compared with NIP ones at extended periods. Moreover, the cytotoxicity of the MIP and NIP NPs samples was evaluated on mesenchymal stem cells, and the obtained observations showed that they had no adverse side effect on the living cells; especially the surface of the MIP NPs sample depicted highly cell's biocompatibility. Finally, the outcomes from designed different experiments conducted us that the HEMA‐based MIP NPs have great potential as an ocular nanocarrier for TM delivery. Copyright © 2016 John Wiley & Sons, Ltd.     

Three‐dimensional remeshed smoothed particle hydrodynamics for the simulation of isotropic turbulence

We present a remeshed particle‐mesh method for the simulation of three‐dimensional compressible turbulent flow. The method is related to the meshfree smoothed particle hydrodynamics method, but the present method introduces a mesh for efficient calculation of the pressure gradient, and laminar and turbulent diffusion. In addition, the mesh is used to remesh (reorganise uniformly) the particles to ensure a regular particle distribution and convergence of the method. The accuracy of the presented methodology is tested for a number of benchmark problems involving two‐ and three‐dimensional Taylor‐Green flow, thin double shear layer, and three‐dimensional isotropic turbulence. Two models were implemented, direct numerical simulations, and Smagorinsky model. Taking advantage of the Lagrangian advection, and the finite difference efficiency, the method is capable of providing quality simulations while maintaining its robustness and versatility.     

Experimental investigation of the wall shear stress and the vortex dynamics in a circular impinging jet

The wall shear stress and the vortex dynamics in a circular impinging jet are investigated experimentally for Re = 1,260 and 2,450. The wall shear stress is obtained at different radial locations from the stagnation point using the polarographic method. The velocity field is given from the time resolved particle image velocimetry (TR‐PIV) technique in both the free jet region and near the wall in the impinging region. The distribution of the momentum thickness is also inspected from the jet exit toward the impinged wall. It is found that the wall shear stress is correlated with the large-scale vortex passing. Both the primary vortices and the secondary structures strongly affect the variation of the wall shear stress. The maximum mean wall shear stress is obtained just upstream from the secondary vortex generation where the primary structures impinge the wall. Spectral analysis and cross-correlations between the wall shear stress fluctuations show that the vortex passing influences the wall shear stress at different locations simultaneously. Analysis of cross-correlations between temporal fluctuations of the wall shear stress and the transverse vorticity brings out the role of different vortical structures on the wall shear stress distribution for the two Reynolds numbers.     

Model‐based analysis of a dielectrophoretic microfluidic device for field‐flow fractionation

We present the development of a dynamic model for predicting the trajectory of microparticles in microfluidic devices, employing dielectrophoresis, for Hyperlayer field‐flow fractionation. The electrode configuration is such that multiple finite‐sized electrodes are located on the top and bottom walls of the microchannel; the electrodes on the walls are aligned with each other. The electric potential inside the microchannel is described using the Laplace equation while the microparticles' trajectory is described using equations based on Newton's second law. All equations are solved using finite difference method. The equations of motion account for forces including inertia, buoyancy, drag, gravity, virtual mass, and dielectrophoresis. The model is used for parametric study; the geometric parameters analyzed include microparticle radius, microchannel depth, and electrode/spacing lengths while volumetric flow rate and actuation voltage are the two operating parameters considered in the study. The trajectory of microparticles is composed of transient and steady state phases; the trajectory is influenced by all parameters. Microparticle radius and volumetric flow rate, above the threshold, do not influence the steady state levitation height; microparticle levitation is not possible below the threshold of the volumetric flow rate. Microchannel depth, electrode/spacing lengths, and actuation voltage influence the steady‐state levitation height.