Macroporous Particles Research Articles

Dynamics of Capillary Electrochromatography: Experimental Study of Flow and Transport in Particulate Beds

AbstractThe chromatographic performance with respect to the flow behavior and dispersion in fixed beds of nonporous and macroporous particles (having mean intraparticle pore diameters of 41, 105, and 232 nm) has been studied in capillary HPLC and electrochromatography. The existence of substantial electroosmotic intraparticle pore flow (perfusive electroosmosis) in columns packed with the macroporous particles was found to reduce stagnant mobile mass transfer resistance and decrease the global flow inhomogeneity over the column cross‐section, leading to a significant improvement in column efficiency compared to capillary HPLC. The effect of electroosmotic perfusion on axial dispersion was shown to be sensitive to the mobile phase ionic strength and mean intraparticle pore diameter, thus, on an electrical double layer interaction within the particles. Complementary and consistent results were observed for the average electroosmotic flow through packed capillaries. It was found to depend on particle porosity and distinct contributions to the electrical double layer behavior within and between particles. Based on these data an optimum chromatographic performance in view of speed and efficiency can be achieved by straightforward adjustment of the electrolyte concentration and characteristic intraparticle pore size.

Chromatographic performance of monodisperse–macroporous particles produced by “modified seeded polymerization.” I: Effect of monomer/seed latex ratio

AbstractIn this study, the monodisperse–macroporous particles produced by a relatively new polymerization protocol, the so‐called, “modified seeded polymerization,” were used as column‐packing material in the reversed phase chromatography (RPC) of proteins. The particles were synthesized in the form of styrene‐divinylbenzene copolymer approximately 7.5 μm in size. In the first stage of the synthesis, the monodisperse polystyrene particles 4.4 μm in size were obtained by dispersion polymerization and used as the “seed latex.” The seed particles were swollen by a low‐molecular‐weight organic agent and then by a monomer mixture. The monodisperse–macroporous particles were obtained by the polymerization of monomer mixture in the seed particles. In the proposed polymerization protocol, the number of successive swelling stages was reduced with respect to the present techniques by the use of sufficiently large particles with an appropriate average molecular weight as the seed latex. A series of particles with different porosity properties was obtained by varying the monomer/seed latex ratio. The separation behavior of HPLC columns including the produced particles as packing material was investigated in the RPC mode using a protein mixture including albumin, lysozyme, cytochrome c, and ribonuclease A. The chromatograms were obtained with different flow rates under an acetonitrile–water gradient. The theoretical plate number increased and chromatograms with higher resolutions were obtained with the particles produced by using a lower monomer/seed latex ratio. The separation ability of the column could be protected over a wide range of flow rates (i.e., 0.5–3 mL/min) with most of the materials tested. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 607–618, 2004

Synthesis and characterizations of monodispersed micron-sized polyaniline composite particles for electrorheological fluid materials

Monodispersed micron-sized polyaniline (PANi) composite particles were synthesized by chemical oxidation polymerization of aniline in the presence of functional porous polymer particles considering the surface functionality and the deposition space. The PANi particles formed in the reaction medium deposited onto the porous substrate to produce PANi-coated composite particles. The formation of the composite was confirmed by Fourier transform IR spectroscopy and UV–vis spectroscopy, and their morphological structures were examined by scanning electron microscopy. From the experimental results, it was determined that PANi was successfully coated onto the functional macroporous polymer particles, maintaining the size monodispersity. The electrorheological properties of the suspensions prepared by dispersing the composite particles in silicone oil were investigated under different electric fields. It was found that the fluids showed a great increase in shear stress, exhibiting a dynamic yield stress under high electric fields; however, the shear stress at low electric fields did not show good particle polarization with fluctuating stress values. In addition, the PANi composite particles exhibited different electrorheological behavior according to the particle size.

Functional, uniform, and macroporous latex particles: Preparation, electron microscopic characterization, and nonspecific protein adsorption properties

Functional, uniform, and macroporous latex particles: Preparation, electron microscopic characterization, and nonspecific protein adsorption properties

Functional, uniform, and macroporous latex particles: Preparation, electron microscopic characterization, and nonspecific protein adsorption properties

AbstractA series of uniform, macroporous particles with different surface chemistries were prepared with different acrylic comonomers [methyl methacrylate (MMA), butyl methacrylate (BMA), epoxypropyl methacrylate (EPMA), 2‐hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA)] with styrene–divinylbenzene (S–DVB) in a multistep seeded polymerization. In the synthesis, uniform polystyrene seed particles 6.2 μm in size were swollen first with a low molecular weight organic agent and then with a monomer phase including an S–DVB mixture and a relatively polar acrylic monomer. Final macroporous particles approximately 10 μm in size were obtained by the repolymerization of the monomer phase in the swollen seed particles. Surface and bulk morphologies were investigated with scanning and transmission electron microscopy, respectively. Although highly porous particles could be achieved with relatively hydrophobic monomers such as styrene, BMA, MMA, and EPMA, the use of hydrophilic monomers such as HEMA and MAA led to the synthesis of uniform particles with lower macroporosity. A comparison of Fourier transform infrared and Fourier transform infrared/diffuse reflectance spectroscopy spectra indicated that the concentration of polar acrylic monomer on the surface was higher than in the bulk structure. The nonspecific protein adsorption behavior of uniform, macroporous particles was investigated with albumin as a model protein. The highest nonspecific albumin adsorption was observed with plain poly(styrene‐co‐divinylbenzene) [poly(S–DVB)] particles. The particles produced with MMA and EPMA also exhibited albumin adsorption capacities very close to that of plain poly(S–DVB). Reasonably low nonspecific albumin adsorption was observed with the particles produced in the presence of MAA, HEMA, and BMA. Poly(S–DVB) particles functionalized with poly(vinyl alcohol) provided nearly zero nonspecific albumin adsorption. For nonspecific albumin binding onto the particles via a physical adsorption mechanism, desorption ratios higher than 80% could be achieved. The desorption ratio with the EPMA‐carrying particles was only 5% because the albumin adsorption onto EPMA‐carrying particles occurred predominantly with covalent‐bond formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 414–429, 2002; DOI 10.1002/app.10412

Characterization of cellulose by SEC-MALLS

Norway spruce (Picea abies) cellulose samplesdissolved in lithium chloride/N,N-dimethyl-acetamide(LiCl/DMAc) covering a wide range of average molecular weights were analyzed bysize exclusion chromatography (SEC) and multi-angle laser light detection(MALLS). The molecular weight distribution of the samples was compared to themolecular weight distribution of cotton linters cellulose samples. To obtaincomplete dissolution of high-molecular-weight wood cellulose, previouslypublished procedures for dissolving cellulose in LiCl/DMAc were modified. SECseparation was performed using macroporous monodisperse polymer particles ascolumn matrix. The refractive index increment (dn/dc)μ forcellulose in 0.5% LiCl/DMAc was found to be 0.104. The radius of gyration,RG, of cellulose in 0.5% LiCl/DMAc depended on the molecular weight,M, according to the relation RG ∝ M0.55. Celluloseprepared from sprucewood by the sulfite cooking process had a broad molecularweight distribution compared to cotton linters cellulose.

2‐Hydroxyethylmethacrylate carrying uniform porous particles: preparation and electron microscopy

AbstractUniform macroporous particles carrying hydroxyl groups have been obtained in the size range 3–11.5 µm by seeded polymerization. For this purpose, uniform polystyrene particles in the size range 1.9–6.2 µm were used as seeds. The seed particles were successively swollen by dibutyl phthalate (DBP) and a monomer mixture comprising styrene, 2‐hydroxyethylmethacrylate (HEMA) and a crosslinker. Two different crosslinkers, divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA), were tested. Size distribution properties together with bulk and surface structures of the particles have been characterized by both scanning and transmission electron microscopy. While EGDMA provides uniform particles with a non‐porous surface, DVB produces uniform particles having a highly porous surface and interior. The comparison of FTIR and FTIR‐DRS spectra shows that the HEMA concentration is higher on the particle surface than within the particle interior. Seed latex size and monomer/seed latex ratios are identified as the most important variables affecting the final particles. Different seed latexes have been tried; the result is that highly macroporous particles with a sponge‐like pore structure both on the surface and in the particle interior have been obtained by use of the seed latex with the largest particles and the lowest molecular weight. An increase in the HEMA feed concentration leads to final particles with a non‐porous surface and a crater‐like porosity in the particle interior. The average pore size significantly decreases with increasing DBP/seed latex and monomer/seed latex ratios.© 2001 Society of Chemical Industry

Carboxyl carrying-large uniform latex particles

Uniform polystyrene particles in the size range of 1.9–6.2 μm were used as the seeds in a multistep polymerization, to produce compact or macroporous particles in the size range of 3–13 μm with reasonably narrow size distributions (i.e. CV<5%). The seed particles with different sizes and molecular weights could be achieved by the dispersion polymerization of styrene. In the synthesis of carboxyl carrying-particles, the seed latices were first swollen by a low molecular weight-organic agent (i.e., dibutylphthalate, DBP), then by styrene (S)–methacrylic acid (MAA)–divinylbenzene (DVB) mixture including an oil-soluble initiator (i.e. benzoyl peroxide, BPO). The final particles were obtained by the polymerization of monomer mixture in the swollen seed particles by keeping the particle uniformity. The average size, size distribution, surface morphology and internal structure of the final beads were evaluated both by scanning and transmission electron microscopy. The average particle size slightly increased with the increasing DBP/seed latex and monomer/seed latex ratios. By keeping the particle uniformity, the size of carboxyl carrying-particles could be adjusted in a relatively wider range (i.e. 3–13 μm) by the selection of seed latex size. Titratable MAA contents between 69 and 181 mg g −1 were found for the particles produced under different conditions. Highly porous and carboxyl functionalized-uniform particles were obtained by starting from the polystyrene seed particles having number-average size and number-average molecular weight of 6.2 μm and 0.58×10 4, respectively. The smaller seed latices with higher molecular weights led to the synthesis of carboxyl carrying-particles with a non-porous surface and an internal part with crater-like porosity. In the case of porous particles, the surface porosity decreased significantly with the decreasing monomer/seed latex ratio and DVB feed concentration. Low monomer/seed latex ratios also resulted in a particle interior with crater-like pore structure.

Complement activation by substituted polyacrylamide hydrogels for embolisation and implantation

An inflammatory reaction has always been observed in vivo around particles used for therapeutic embolisation. Hydrogel microspheres based on Trisacryl ®, prepared by polymerisation of N-acryloyl-2-amino-2-(hydroxymethyl)-1,3-propanediol in the presence of a crosslinking agent, are amongst the best materials for such a purpose. The aim of this work was to evaluate in vitro the complement-activating capacity of the OH-bearing Trisacryl ® particles either microporous, or macroporous, or partially substituted with carboxylate, or diethylaminoethyl, or sulphonate groups, in order to be able to decrease the inflammatory reaction in vivo. Complement was activated in the presence of Trisacryl ®, but about seven times less than in the presence of Sephadex ®, despite a quasi-similar density in OH groups, and more than two times less than in the presence of hydroxymethylated polystyrene despite a higher OH density. This demonstrates that not only OH density, but also other features linked to the type of polymeric backbone, are involved in complement activation by OH-bearing polymeric surfaces. The microporous and macroporous particles activated complement at a similar level when crushed and a slight increase was observed on the rough surface of the macroporous microspheres, but the presence of the macropores did not increase complement activation. Concerning the effects of substituting groups on Trisacryl ®, a clear decrease in the complement activation has been found only in the presence of sulphonate groups.

MECHANISMS AND KINETICS OF HIGH-TEMPERATURE CADMIUM SORPTION BY PACKED BED OF CALCINED KAOLIN

Sorption experiments by passing CdCl2-carrying flue gas through the packed bed of calcined macro-porous kaolin particles were performed over a temperature range of 973–1173 K and a CdCl2 partial pressure range of 8–16.1 Pa. The observed structural change of the sorbent mineral at the stage of sorption and the results of desorption tests revealed the characteristics of an irreversible chemical reaction as a major cadmium capturing mechanism. In the fully saturated kaolin sorbent, CdO·Al2O·2SiO2 is present as a sorption reaction product together with a smaller amount of 2CdO·Al2O·2SiO2. The increase in sorbent bed temperature resulted in an increase in the rate of sorption, but it had no effect on maximum cadmium uptake. The gas-phase CdCl2 diffusion into the macro pores of calcined kaolin had a negligible effect on the overall sorption rate. The reaction between gaseous CdCl2 and solid Al2O3.2SiO2 is very sensitive to the concentration of CdCl2 but relatively insensitive to the temperature of the sorbent bed. The order of reaction with respect to the CdCl2 vapor concentration was determined to be 3.26. The activation energy, Ea , was estimated as 5.56 kcal/mol according to the Arrhenius relationship.

Ordered Macroporous Particles by Colloidal Templating

Ordered macroporous particles of silica and titania were fabricated by colloidal templating. The colloidal templates were assembled through colloidal crystallization of suspended polystyrene latex sphere particles in aqueous droplets straddling an air−oil interface. The procedures involve first preparing spherical colloidal crystalline particles of polystyrene latex spheres and then infusing them with metal precursor solutions that form silica or titania in the interstices. Finally, calcination decomposes the polystyrene latex spheres, leaving macropores at their sites. The shape of the template was controlled by the presence of additive surfactant or by the action of an applied electric field. Specifically, spherical, concaved disklike, and ellipsoidal colloidal crystals were prepared successfully and used as templates for the fabrication of ordered macroporous particles. The SEM images of the prepared macroporous particles showed that the pores were interconnected and ordered into a hexagonal arrangement.

Chromatographic behavior of macroporous particles in electroendoosmotically and pressure driven liquid chromatography

The potentials of wide-pore particles are studied in electrochromatography (CEC) and in pressure driven flow (HPLC). The H-u curves are studied for three types of stationary phases. When the pore diameter is large enough (4000A or 1000A) high flow is occurring through the pores resulting in decrease of flow inhomogeneities and in suppression of stagnant mobile phase pools into which solute molecules would diffuse. The performances of the columns were evaluated in CEC and in HPLC and higher efficiencies were obtained in CEC. In CEC, the effect of ionic strength and pore diameter on efficiencies was investigated in term of double layer overlap. Columns packed with 7 μm particles with a pore diameter of 4000A generated about 650,000 theoretical plates m−1 which corresponds to a reduced theoretical plate height of 0.2. In HPLC, the influence of column diameter on efficiencies was also studied. It has been shown that with macroporous particles, the reduction of column diameter led to improvement of column efficiency.

Assessment of Electroosmotic Perfusion in Capillary Chromatographic Columns Using Electrical Conductivity

The electrical conductivity of capillary electrochromatography (CEC) columns packed with macroporous particles has been investigated. Columns were prepared with commercially available octadecylsilane-coated 7 μm diameter particles (Nucleosil) having nominal pore diameters of 100, 300, 500, 1000, and 4000 Å, and operated under typical CEC conditions. The conductivity of the 100 Å column was in agreement with that predicted from theory for nonporous spheres, indicating that intraparticle current was negligible. Columns packed with the wide-pore media (1000 Å and 4000 Å), in contrast, yielded conductivity values over 2-fold greater than the 100 Å. The electroosmotic contribution to current flow in these columns was deemed insignificant on the basis of theoretical modeling and the experimental data. It was therefore concluded that the increased column conductivity of the wide-pore packed columns was the result of intraparticle current transport. These results further suggest that wide-pore packings are more permeable to fluid flow and thus can provide maximum gains in efficiency due to electroosmotic perfusion when electrical double layer thickness is small relative to the median pore diameter of the packing.

SIZE EXCLUSION CHROMATOGRAPHY OF CELLULOSE DISSOLVED IN LiCl/DMAC USING MACROPOROUS MONODISPERSE POLY(STYRENE-CO-DIVINYLBENZENE) PARTICLES

Two types of hydrophilic macroporous monodisperse particles (MMP) based on poly(styrene-co-divinylbenzene) have been investigated for use as column material for size exclusion chromatography (SEC) analysis of cellulose dissolved in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). The particles appeared inert to the mobile phase and no adsorption of cellulose could be detected. Favorable chromatographic properties associated with monosized particles such as low back pressures and high flow rates were obtained. Two MMP columns of different pore size distributions coupled in series, allowed separation of cellulose in the molecular weight range 104–107 g/mole. The particles were suitable for SEC of cellulose samples dissolved in 0.5% LiCl/DMAc and the reproducibility and long term stability were superior to that of a comparable commercial SEC column.

Modeling interparticle and intraparticle (perfusive) electroosmotic flow in capillary electrochromatography

A model to estimate the extent of intraparticle, or perfusive, electroosmotic flow (EOF) in CEC capillaries packed with macroporous particles has been developed. Nucleosil packings (d(p) = 7 microm) having nominal pore sizes of 500, 1000, and 4000 A were studied. Intraparticle pores ranging from 50 to 10000 A in diameter were partitioned into 995 intervals of 10 A. Using pore size distribution data for the sorbents obtained by mercury intrusion porosimetry, fractions of the total column void volume contributed by pores in the range of interest were determined. The average channel diameter of the interstitial space was estimated from the d(p) of the packing; its fraction of total column volume was determined from the interstitial porosity. Estimations of relative EOF velocity in the intraparticle and interstitial channels were made by treating the channels as parallel cylindrical capillary tubes. Relative EOF values were combined with the volume fraction data and used as weighting factors in calculating an effective particle diameter (d(p,eff)) for each set of conditions (i.e., packing type, ionic strength of eluent). Values of d(p,eff) generated by the model correctly predict the trends observed in the experimental data. At the lowest ionic strength, plate height correlated inversely with the pore size of packing (h4000 A < h1000 A < h500 A). Rate curves for each column tended toward lower plate heights with increasing eluent ionic strength before converging at some limiting point. The point of convergence was reached at moderate ionic strengths for the larger pore media (1000 and 4000 A) and higher ionic strength for the 500 A.

Isolation of Single-Stranded DNA Using Denaturing DNA Chromatography

Ion pair reverse-phase liquid chromatography has been widely employed for nucleic acid separations. A wide range of alternative stationary phases have been utilised in conjunction with ion pair reverse-phase chromatography, including totally porous particles, non-porous particles, macroporous particles and monolithic stationary phases. In this study we have utilised superficially porous silica particles in conjunction with ion pair reverse-phase liquid chromatography for the analysis of nucleic acids. We have investigated a range of different pore-sizes and phases for the analysis of a diverse range of nucleic acids including oligonucleotides, oligoribonucleotides, phosphorothioate oligonucleotides and high molecular weight dsDNA and RNA. The pore size of the superficially porous silica particles was shown to significantly affect the resolution of the nucleic acids. Optimum separations of small oligonucleotides such as those generated in RNase mapping experiments were obtained with 80 Å pore sizes and can readily be interfaced with mass spectrometry analysis. Improved resolution of larger oligonucleotides (>19 mers) was observed with pore sizes of 150 Å. The optimum resolution for larger dsDNA/RNA molecules was achieved using superficially porous silica particles with pore sizes of 400 Å. Furthermore, we have utilised 150 Å pore size solid-core particles to separate typical impurities of a fully phosphorothioated oligonucleotide, which are often generated in the synthesis of this important class of therapeutic oligonucleotide.

Capillary electrochromatography with macroporous particles

The performance of macro-porous particles in capillary electrochromatography is studied. Three reversed-phase stationary phases with pore diameters between 500 Å and 4000 Å have been tested for separation efficiency and mobile phase velocity. With these stationary phases, a large portion of the total flow appears to be through the pores of particles, thereby increasing the separation efficiency through a further decrease of the flow inhomogeneity and through enhancement of the mass transfer kinetics.The effects of pore size and mobile phase composition on the plate height and mobile phase velocity have been studied. With increasing buffer concentrations and larger pore diameters, higher mobile phase velocities and higher separation efficiencies have been obtained.Columns packed with 7 μm particles containing pores with a diameter of 4000 Å generated up to 430 000 theoretical plates/m for retained compounds. Reduced plate heights as low as 0.34 have been observed, clearly demonstrating that a significant portion of the flow is through the pores. For the particles containing 4000 Å pores no minimum was observed in the H-u plot up to linear velocities of 3.3 mm/s, suggesting that the separation efficiency is dominated by axial diffusion. On relatively long (72 cm) columns, efficiencies of up to 230 000 theoretical plates/column have been obtained under non-optimal running conditions. On short (8.3 cm) columns fast separations could be performed with approximately 15 000 theoretical plates generated in less than 30 s.

Determination of the effective diffusion coefficient for gold(III) on a macroporous resin XAD-2 impregnated with triisobutyl phosphine sulfide

In this work the experimental and numerical techniques employed to estimate the diffusion coefficient of gold(III) in a macroporous particle of resin XAD-2 impregnated with triisobutyl phosphine sulfide (TIBPS) have been described. Batch and column experiments were performed in order to get the necessary experimental results to determine the effective diffusion coefficient, D e . In the studied initial metal concentration range (39.3–196 mg/dm 3), D e was found to increase with increasing the initial feed concentration from 1.28×10 −8 to 6.40×10 −8 m 2/h.

Electron microscopic observation of uniform macroporous particles. I. effect of seed latex type and diluent

Electron microscopic observation of uniform macroporous particles. I. effect of seed latex type and diluent

Electron microscopic observation of uniform macroporous particles. I. effect of seed latex type and diluent

Uniform and macroporous polymer particles in the size range of 5–21 μm were prepared by a multistep seeded polymerization method. The uniform polystyrene particles in the size range of 1.9–7.5 μm were used as the seed particles in the preparation of macroporous beads. The seed particles with different sizes and molecular weights were produced by dispersion polymerization, by changing the type of dispersion medium and the initiator concentration. In the synthesis of macroporous particles, a two-step swelling procedure was employed. The seed latexes were first swollen by a low molecular-weight organic agent (i.e., dibutyl phthalate, DBP), then by a divinylbenzene–ethylvinylbenzene isomer mixture including an oil phase soluble initiator (i.e., benzoyl peroxide). The porous structure in the final beads was achieved by the polymerization of the monomer phase within the swollen seed particles including a mixture of linear polystyrene and DBP. The initiator concentration in the repolymerization step, the seed latex type (i.e., the diameter and the molecular weight of seed latex), DBP/seed latex, and the monomer/seed latex ratios were changed to achieve uniform polymer beads with different average sizes and pore structures. The average size, the size distribution, and the surface morphology of final beads were analyzed by Scanning Electron Microscopy. The internal structure of the beads were analyzed by Transmission Electron Microscopy. The results indicated that the average size of the final particles increased with increasing the seed latex diameter, DBP/seed latex, and monomer/seed latex ratios. The average pore size decreased with decreasing the molecular weight of the seed latex and increasing the DBP/seed latex and monomer/seed latex ratios. These tendencies were explained by the viscosity change of the porogen solution used in the repolymerization step. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2271–2290, 1999