Comparison of particle size and flow rate optimization for chromatography using one-monomer molecularly imprinted polymers versus traditional non-covalent molecularly imprinted polymers

The dependence of enantio-selective chromatographic performance on particle size, as measured by separation factor, was investigated for one-monomer molecularly imprinted polymers (OMNiMIPs) compared to traditionally formed EGDMA/MAA molecularly imprinted polymers (MIPs). Five particle size ranges were compared (<20 μm, 20-25 μm, 25-38 μm, 38-45 μm, and 45-63 μm), revealing that the particle sizes above 25 μm provided the highest separation factor, and thus the best enantiomer separation, for both imprinted polymers. Other chromatographic parameters such as the number of theoretical plates and resolution exhibited only minor changes for the OMNiMIPs as the particle size changed, except for particles 20 μm and below. However, the number of theoretical plates and resolution for EGDMA/MAA are higher for particles in the 20-25 μm range. Thus, chromatographic factors for the EGDMA/MAA polymers are better in this range, despite better enantioselectivity for particle sizes above 25 μm. In contrast, OMNiMIPs generally show the most favorable performance for particle sizes in the 38-45 μm range. It was also found that decreasing flow rate resulted in improved enantioselectivity for both MIPs for all particle sizes.     

Effect of the presence of polymer in miniemulsion droplets on the kinetics of polymerization

Solution of polystyrene in styrene were dispersed in an aqueous gel phase comprising sodium lauryl sulfate, cetyl alcohol, and water using an emulsification process known to produce monomer droplet sizes inthe submicron size range (referred to as miniemulsion droplets). The shelf-life stabilities of these miniemulsions were studied to determine their relative droplet sizes, and the emulsions were concommitantly polymerized in an isothermal batch reaction calorimeter. The polymerization kinetics and final particle sizes produced were compared with miniemulsion and conventional emulsion polymerizations prepared using equivalent recipes without the addition of polystyrene. The results indicate that polymerization of miniemulsions prepared from polymer solutions produce significantly different kinetics than both miniemulsion and conventional emulsion polymerizations. In general, a small amount of polymer greatly increases the rate of polymerization and the final number of particles produced in the polymerization to the extent where even conventional polymerizations carried out above the critical micelle concentration of the surfactant polymerize more slowly. The results are explained by considering the system to be comprised of small, stable pre-formed monomer-swollen polymer particles which are able to efficiently capture aqueous phase radicals. This enables the system to produce a large final number of particles, similar to the initial number of pre-formed polymer particles, as opposed to miniemulsions and micelles in which only a relatively small fraction of the initial number of species (droplets or micelles) become polymer particles. © 1994 John Wiley & Sons, Inc.     

Creaming Stability of Flocculated Monodisperse Oil-in-Water Emulsions

The influence of droplet flocculation on the creaming stability of monodisperse n-hexadecane oil-in-water emulsions was studied. The creaming velocity of emulsions with different droplet radii (0.43 and 0.86 μm), droplet concentrations (1-67 vol%), and sodium dodecyl sulfate (SDS) concentrations (7-80 mM) were measured. Depletion flocculation was observed in the emulsions when the aqueous phase SDS concentration exceeded a particular level ( approximately 40 mM for 0.43-μm droplets and approximately 15 mM for 0.86-μm droplets). Creaming was monitored by measuring the back-scattered light from an emulsion as a function of its height. The creaming velocity increased with increasing flocculation and decreased with increasing droplet concentration. These results have important implications for the formulation of emulsion-based materials. Copyright 2000 Academic Press.     

Effect of adding anionic surfactant on the stability of Pickering emulsions

We investigated the structure and stability of dodecane-in-water emulsions stabilised by partially hydrophobised silica particles after dilution of the emulsions in solutions of sodium dodecyl sulfate and sodium chloride. The emulsions were stable to coalescence on dilution in salt solutions, but did cream over time. The rate and extent of creaming gradually decreased as the salt concentration in the diluted emulsion increased. Dilution in low concentrations of the anionic surfactant did not affect the emulsion stability to coalescence or alter the creaming behaviour of the emulsion. At surfactant concentrations above the critical micelle concentration, however, the rate and extent of creaming and flocculation of the drops were enhanced.     

Enzymatic Saccharification and Viscosity of Sawdust Slurries Following Ultrasonic Particle Size Reduction

Results in a previous study showed up to a 55% increase in saccharification rates when the initial particle size range decreased from 590?<?x?<?850 μm down to 33?<?x?<?75 μm. The smaller particle sizes also lowered the viscosity of the slurry 50-fold (for an equivalent initial solids concentration). In this study, ultrasonic irradiation was employed to further reduce the particle size of sawdust slurries below the ranges in the previous study in an attempt to further increase enzymatic saccharification rates and lower the slurry viscosity. Average particle sizes were reduced to less than 1 μm under the conditions tested. Surprisingly, the amount and rates of sugar released in this study with the ~1 μm particles is comparable (maximum glucose release of 30%) to, but no better than that seen for particle sizes in the range of 33?≤?x?≤?75 μm (maximum glucose release of 31%). Also surprisingly, the viscosity increased as the average particle sizes in the slurries decreased, which is opposite to the trend in the previous study. For example, there was an approximately threefold increase in the viscosity between unsonicated samples with a range of 10?≤?x?≤?75 μm and sonicated samples with a range of 0.05?≤?x?≤?12 μm. This is attributed to the variations in surface characteristics of the particles which were characterized here using X-ray diffraction profiles and SEM pictures.     

Microwave-assisted nitroxide-mediated miniemulsion polymerization of styrene

Nitroxide-mediated free-radical miniemulsion polymerizations (NMRPs) of styrene were successfully performed under microwave irradiation at 135 °C. The polymerizations proceeded in a controlled manner, yielding polymers that showed an incremental increase in molecular weight with conversion and had narrow molecular weight distributions. The resulting latexes were colloidally stable. The polymerization behavior, molecular weights of polymers and Z-average size of latex particles were also investigated under two different heating methods, microwave irradiation and conventional heating.     

An experimental investigation of creaming phenomenon using a novel optical method: A case study of mineral oil-in-water emulsion

The present study elucidates the creaming phenomenon of mineral oil-in-water macroemulsion using a new noninvasive method based on turbidimetry. Additionally, microscopic observation of the phenomenon is carried out to derive an in-depth understanding of the mechanisms. Accumulation of the particles in the emulsions under the formed cream is monitored during a relatively prolonged period of time. Backflow of continuous and dispersed phases in temporary channels is observed at the proximity of the cream. In addition to the backflow, a high traffic density of the dispersed particles and deflocculation of the cream are the main reasons for the accumulation of the dispersed phase particles and a temporary stability against creaming. The deflocculation hinders cream growth and increases the stratification of the cream. A low concentration zone of the dispersed phase with the width of ～100?µm is observed under the cream.     

Particle size effects of carbon sources on electrochemical properties of LiFePO<Subscript>4</Subscript>/C composites

Carbon-coated LiFePO₄ cathode materials were prepared by a solid-state method incorporating different sizes of polystyrene (PS) spheres as carbon sources. In scanning electron microscope images, small PS spheres appear more effective at preventing aggregation of LiFePO₄ particles. From transmission electron microscopy images, it was found that the LiFePO₄ particles were completely uniformly coated with 5-nm carbon layer when the carbon source was 0.22 μm PS spheres. When the size of PS sphere was increased to 2.75 μm, a network of carbon was formed and wrapped around the LiFePO₄ to create a conductive web. Raman spectroscopy and four-point probe conductivity measurement showed that using larger sizes of PS spheres as carbon sources leads to greater conductivity of LiFePO₄/C. The LiFePO₄ precursor sintered with 0.22 μm PS spheres delivered an initial discharge capacity of 145 mAh g^?1 at a 0.2 C rate, but it only sustained 289 cycles at 80% capacity. When the diameter of PS spheres was increased to 2.75 μm, the discharge capacity of LiFePO₄/C decreased, but the cycle life reached 755 cycles, the highest number in this work probably due to the network formation of carbon wrapping around LiFePO₄ particles.     

Oil-in-water emulsions stabilized by whey protein aggregates: Effect of aggregate size,pH of aggregation and emulsion pH

Oil-in-water emulsions (60% oil (w/w)) were prepared using whey protein aggregates as the sole emulsifying agent. The effects of whey protein aggregate size (the diameter between 0.92 and 10.9?µm), the pH of emulsions (4–8.6) and storage time on physical properties, droplet size, and stability of emulsions were investigated. The results indicate that increment of whey protein aggregate size caused an increase in the firmness, droplet size, and viscosity of emulsions, and also a decrease in the emulsion creaming. The emulsion viscosity, firmness, and droplet size were reduced by increasing the emulsion pH; however, the creaming process was accelerated. Viscosity, creaming, and droplet size of emulsions were increased slightly during 21 days storage at 40°C.     

1.1 μm superficially porous particles for liquid chromatography. Part I: synthesis and particle structure characterization

Superficially porous particles are characterized by a non-porous particle core surrounded by a thin porous layer. Superficially porous particles have been shown to have chromatographic advantages over traditional totally porous particles by reducing the resistance to mass transfer and the eddy diffusion contributions to the theoretical plate height, particularly for biomolecule separations. Currently, 1.7 μm superficially porous particles are commercially available, but a further decrease in the particle diameter and reduction in the porous layer thickness has the potential to further improve the efficiency of the column packing material. In this study, the synthesis of smaller diameter superficially porous particles was investigated. As the particle diameter was decreased, however, synthesis parameters previously reported were rendered unsuitable due to particle agglomeration, non-uniform coating, and porous layer disintegration. Parameters such as colloidal silica size, drying process, and sintering temperature were investigated to improve the structural characteristics of smaller diameter superficially porous particles. Reported is a synthetic route for production of 1.1 μm superficially porous particles having a 0.1 μm porous layer. Based on the revised method, the particles produced have a surface area, pore diameter, and particle size distribution RSD of 52 m²/g, 71 Å, and 2.2%, respectively.     

The combustion synthesis of iron group metal fine powders

The new approach has been developed for the synthesis of nickel (Ni), cobalt (Co) and iron (Fe) powders from the appropriate oxides by the solid combustion method. The reduction was made by sodium azide (NaN₃) at the presence of carbon in the argon atmosphere. The variation of combustion temperature and velocity was performed by using alkali metal salt as an inert diluent. The values of combustion parameters were measured and also the temperature distribution in a combustion wave are obtained. The geometric sizes of reactionary zones and the activation energy of the process were estimated. The optimum conditions for single-phase metal powder synthesis were found. Powders fabricated in this way had cubic structure and particles size about 0.5-2.0 μm for Ni, Co and 1-3 μm for Fe. In a number of cases the formation of spherical particles with the average size about 5-15 μm were observed.     

Gas chromatography for in situ analysis of a cometary nucleus. IV. Study of capillary column robustness for space application

As part of the development of the European Space Agency Rosetta space mission to investigate a cometary nucleus, the selection of columns dedicated to the gas chromatographic subsystem of the Cometary Sampling and Composition (COSAC) experiment was achieved. Once the space probe launched, these columns will be exposed to the harsh environmental constraints of space missions: vibrations, radiation (by photons or energetic particles), space vacuum, and large temperature range. In order to test the resistance of the flight columns and their stationary phases, the columns were exposed to these rough conditions reproduced in the laboratory. The comparison of the analytical performances of the columns, evaluated prior and after the environmental tests, demonstrated that all the columns withstand space constraints, and that their analytical properties were preserved. Therefore, all the selected capillary columns, even having porous layer or chiral stationary phases, were qualified for space exploration.     

Factors affecting membrane fouling reduction by surface modification and backpulsing

Several factors affecting microfiltration membrane fouling and cleaning, including backpulsing, crossflushing, backwashing, particle size, membrane surface chemistry, and ionic strength, were investigated with suspensions of latex beads. Approximately two-fold permeate volume enhancements over 1 h of filtration were obtained by using water or gas backpulsing, and 50% enhancement was obtained with crossflushing, for filtration of 1.0 μm diameter carboxylate modified latex (CML) particles using unmodified polypropylene (PP) membranes of 0.3 μm nominal pore diameter. When 0.2 μm diameter CML particles or mixtures of 1.0 and 0.2 μm CML particles were used, however, the average flux decreased 60% compared with using 1.0 μm CML particles for experiments with or without backpulsing.PP membranes were rendered hydrophilic with neutral or positively on negatively charged surfaces by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively, to the base PP membranes. Filtration experiments show that fouling is not strongly dependent on membrane surface chemistry for filtration of 1.0 μm CML particles without backpulsing. With backpulsing, however, a 10% increase and a 20% decrease of permeate volumes collected in 1 h were observed when the CML particles and the membranes had like charges and opposite charges, respectively, compared to the permeate collected with the unmodified membrane. Using the PP membranes modified with AA, permeate volumes with backpulsing decreased 30 and 40% when NaCl concentrations of 0.01 and 0.1 M, respectively, were added to the feed. However, the permeate volumes did not vary significantly with changing ionic strength for filtration without backpulsing.     

Core–shell column Tanaka characterization and additional tests using active pharmaceutical ingredients

In the last decade, core–shell particles have gained more and more attention in fast liquid chromatography separations due to their comparable performance with fully porous sub‐2 μm particles and their significantly lower back pressure. Core–shell particles are made of a solid core surrounded by a shell of classic fully porous material. To embrace the developed core–shell column market and use these columns in pharmaceutical analytical applications, 17 core–shell C₁₈ columns purchased from various vendors with various dimensions (50 mm × 2.1 mm to 100 mm × 3 mm) and particle sizes (1.6–2.7 μm) were characterized using Tanaka test protocols. Furthermore, four selected active pharmaceutical ingredients were chosen as test probes to investigate the batch to batch reproducibility for core–shell columns of particle size 2.6–2.7 μm, with dimension of 100 × 3 mm and columns of particle size 1.6 μm, with dimension 100 × 2.1 mm under isocratic elution. Columns of particle size 2.6–2.7 μm were also tested under gradient elution conditions. To confirm the claimed comparable efficiency of 2.6 μm core–shell particles as sub‐2 μm fully porous particles, column performances of the selected core–shell columns were compared with BEH C₁₈, 1.7 μm, a fully porous column material as well.     

Size effects of discoidal PLGA nanoconstructs in Pickering emulsion stabilization

Solid particle stabilized emulsions, using unique shape defined particles, are receiving increasing research interest due to ease of formulation and interesting physiochemical characteristics. There is, however, a need to systematically investigate the effect of anisotropic discoidal microparticles, realized with top-down fabrication approaches, in emulsion stabilization. Here, the effect of poly(d ,l -lactide-co-glycolide) (PLGA) discoidal polymeric nanoconstruct (DPN) size on the formation and stability of oil-in-water emulsions is studied. Particles with a diameter of 1, 2, and 5 μm are fabricated with a lithographic templating technique, and used to stabilize medium chain triglyceride (MCT) oil emulsions. Three phase contact angles decreased from 85° ± 7° to 68° ± 12° moving from 1 to 5 μm DPN stabilized emulsions, showing a particle “hydrophilicity” increase with size. Microscopy imaging showed that the mean droplet diameter and dispersity increased with particle size, and that DPNs were present at the oil–water interface. DPN based emulsions were stable for about 24 h or less in the case of 1 and 2 μm DPNs. Emulsion stability was shorter than 12 h in case of 5 μm DPNs. Finally, calculations of DPN detachment free energies ΔG_dw and excess surface coverages C_excess demonstrated that, despite the significantly high adhesion energy of the discoidal DPN, emulsion stability was mostly affected by gravitational forces for DPN sizes above 2 μm. The use of PLGA and MCT oil in this study is relevant for future use of Pickering emulsions in pharmaceutical and drug delivery applications.     

Deterministic Ratchets for Particle Separation Fabricated With Si MEMS Technology

This paper presents the design, fabrication and testing of deterministic ratchets which are used for fractionation purpose. Ratchets with different configuration are prepared to determine particle trajectories with different sizes. Silicon based MEMS technology is used to fabricate devices containing arrays of obstacles with varying size, spacing and number. The arrays of high aspect ratio, 7-20μm wide, silicon pillars are defined and etched in 60 to 80μm deep microchannels using Deep Reactive Ion Etching (DRIE). The working modes of the ratchets are demonstrated using colloidal suspensions of latex particles which have an average diameter ranging between 2 and 6μm.     

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究朱世雄杜金环金熹高陈柳生（中国科学院化学研究所北京１０００８０）关键词无乳化剂乳液聚合，单分散，均相成核，低聚物胶束微米级大粒径单分散高分子微球在标准计量、情报信息、分析化学等许多领域都有广泛的...     

Rapid identification of erythrocyte phospholipids in Sprague–Dawley rats by ultra high performance liquid chromatography with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry

A rapid, sensitive, and reliable approach for analyzing five kinds of erythrocyte phospholipids in Sprague–Dawley rats was provided by ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry with MassLynx^TM MassFragment. Improving conventional high performance liquid chromatography techniques, ultra high performance liquid chromatography integrated with quadrupole time‐of‐flight tandem mass spectrometry offers high sensitivity and increased analytical speed by using columns packed with sub‐2 μm particles (1.7 μm), which allows a faster separation to be achieved. Through this method, 83 phospholipids were tentatively characterized based on their mass spectra and tandem mass spectra, as well as by matching the in‐house formula database within a mass error of 5 ppm, including 40 phosphatidylcholines, 24 phosphatidyl ethanolamines, three phosphatidylinositols, six phosphatidylserines, and ten sphingomyelins. Our present results proved that the established method could be used to qualitatively analyze complex erythrocyte phospholipids in Sprague–Dawley rats and provide a useful data base for pharmacology and phospholipidomics to seek potential biomarkers of disease prediction.     

A model to describe the settling behavior of fractal aggregates

A model to predict fractal dimension from sedimentating fractal aggregates has been successfully developed. This model was developed using the settling rate and size data of fractal aggregates. In order to test the validity of the model, a purpose-built settling rig, equipped with lens with magnification of 1200x, which can capture images of particles/flocs down to 2 microm in diameter was used. The performance and technique of the settling rig were validated by comparing the measured settling rates of 30- and 50.7-microm standard particles with their theoretical settling rates calculated using Stokes' law. The measured settling rates were within 10% agreement with the calculated Stokes' velocities. The settling rates and sizes of the particles/flocs were analyzed using image analysis software called WiT 5.3. The maximum temperature gradient across the settling column was 0.1 degrees C, which effectively eliminated convective currents due to temperature differences in the settling column. A total of 1000 calcium phosphate flocs were analyzed. Calcium phosphate flocs with fractal dimensions varying from 2.3 to 2.8 were generated via orthokinetic aggregation. Measurements of fractal dimensions, using light scattering, were done simultaneously with the settling experiments and they were found to be constant. The fractal dimensions calculated using the model agreed with those obtained by light scattering to within 12%.     

Visible-Light Initiated Dispersion Photopolymerization of Styrene

Polystyrene (PS) particles were synthesized in ethanol/water mixture by dispersion polymerization using visible light irradiation, with either a N-heterocyclic carbene borane-based photoinitiating system (PIS) or a disulfide. With the full PIS and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as stabilizer, the size distributions were broad and the amount of PEGMA had a strong impact on the experiment reproducibility. The addition of a base solved the problem, leading to faster polymerizations, narrower size distributions and larger particles. With the disulfide as sole PIS, bigger and narrowly distributed PS particles were again formed. Quantitative conversion was achieved in each system, with particle size ranging between 100 and 350 nm. The use of poly(N-vinylpyrrolidone) as stabilizer led to significantly larger particles, up to 1.2 μm, with narrow size distributions. The production of such large latex particles by photoinitiated polymerizations is unprecedented.