C18‐bound porous silica monolith particles as a low‐cost high‐performance liquid chromatography stationary phase with an excellent chromatographic performance

Ground porous silica monolith particles with an average particle size of 2.34 μm and large pores (363 Å) exhibiting excellent chromatographic performance have been synthesized on a relatively large scale by a sophisticated sol–gel procedure. The particle size distribution was rather broad, and the d(0.1)/d(0.9) ratio was 0.14. The resultant silica monolith particles were chemically modified with chlorodimethyloctadecylsilane and end‐capped with a mixture of hexamethyldisilazane and chlorotrimethylsilane. Very good separation efficiency (185 000/m) and chromatographic resolution were achieved when the C₁₈‐bound phase was evaluated for a test mixture of five benzene derivatives after packing in a stainless‐steel column (1.0 mm × 150 mm). The optimized elution conditions were found to be 70:30 v/v acetonitrile/water with 0.1% trifluoroacetic acid at a flow rate of 25 μL/min. The column was also evaluated for fast analysis at a flow rate of 100 μL/min, and all the five analytes were eluted within 3.5 min with reasonable efficiency (ca. 60 000/m) and resolution. The strategy of using particles with reduced particle size and large pores (363 Å) combined with C₁₈ modification in addition to partial‐monolithic architecture has resulted in a useful stationary phase (C₁₈‐bound silica monolith particles) of low production cost showing excellent chromatographic performance.     

Rapid determination of parabens in seafood sauces by high‐performance liquid chromatography: A practical comparison of core–shell particles and sub‐2 μm fully porous particles

In this work, the chromatographic performance of superficially porous particles (Halo core–shell C₁₈ column, 50 mm × 2.1 mm, 2.7 μm) was compared with that of sub‐2 μm fully porous particles (Acquity BEH C₁₈, 50 mm × 2.1 mm, 1.7 μm). Four parabens, methylparaben, ethylparaben, propylparaben, and butylparaben, were used as representative compounds for calculating the plate heights in a wide flow rate range and analyzed on the basis of the Van Deemter and Knox equations. Theoretical Poppe plots were constructed for each column to compare their kinetic performance. Both phases gave similar minimum plate heights when using nonreduced coordinates. Meanwhile, the flat C‐term of the core–shell column provided the possibilities for applying high flow rates without significant loss in efficiency. The low backpressure of core–shell particles allowed this kind of column, especially compatible with conventional high‐performance liquid chromatography systems. Based on these factors, a simple high‐performance liquid chromatography method was established and validated for the determination of parabens in various seafood sauces using the Halo core–shell C₁₈ column for separation.     

Characterization and kinetic performance of 2.1 × 100 mm production columns packed with new 1.6 μm superficially porous particles

The overall kinetic performance of three production columns (2.1 mm × 100 mm format) packed with 1.6 μm superficially porous CORTECS‐C₁₈+ particles was assessed on a low‐dispersive I‐class ACQUITY instrument. The values of their minimum intrinsic reduced plate heights (h_min = 1.42, 1.57, and 1.75) were measured at room temperature (295 K) for a small molecule (naphthalene) with an acetonitrile/water eluent mixture (75:25, v/v). These narrow‐bore columns provide an average intrinsic efficiency of 395 000 plates per meter. The gradient separation of 14 small molecules shows that these columns have a peak capacity about 25% larger than similar ones packed with fully porous BEH‐C₁₈ particles (1.7 μm) or shorter (50 mm) columns packed with smaller core–shell particles (1.3 μm) operated under very high pressure (>1000 bar) for steep gradient elution (analysis time 80 s). In contrast, because their permeabilities are lower than those of columns packed with larger core–shell particles, their peak capacities are 25% smaller than those of narrow‐bore columns packed with standard 2.7 μm core–shell particles.     

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.     

Using light scattering to evaluate the separation of polydisperse nanoparticles

The analysis of natural and otherwise complex samples is challenging and yields uncertainty about the accuracy and precision of measurements. Here we present a practical tool to assess relative accuracy among separation protocols for techniques using light scattering detection. Due to the highly non-linear relationship between particle size and the intensity of scattered light, a few large particles may obfuscate greater numbers of small particles. Therefore, insufficiently separated mixtures may result in an overestimate of the average measured particle size. Complete separation of complex samples is needed to mitigate this challenge. A separation protocol can be considered improved if the average measured size is smaller than a previous separation protocol. Further, the protocol resulting in the smallest average measured particle size yields the best separation among those explored. If the differential in average measured size between protocols is less than the measurement uncertainty, then the selected protocols are of equivalent precision. As a demonstration, this assessment metric is applied to optimization of cross flow (V_x) protocols in asymmetric flow field flow fractionation (AF⁴) separation interfaced with online quasi-elastic light scattering (QELS) detection using mixtures of polystyrene beads spanning a large size range. Using this assessment metric, the V_x parameter was modulated to improve separation until the average measured size of the mixture was in statistical agreement with the calculated average size of particles in the mixture. While we demonstrate this metric by improving AF⁴V_x protocols, it can be applied to any given separation parameters for separation techniques that employ dynamic light scattering detectors.     

Characterization of new types of stationary phases for fast and ultra-fast liquid chromatography by signal processing based on AutoCovariance Function: A case study of application to Passiflora incarnata L. extract separations

In this study, a comparative investigation was performed of HPLC Ascentis^® (2.7 μm particles) columns based on fused-core particle technology and Acquity^® (1.7 μm particles) columns requiring UPLC instruments, in comparison with Chromolith™ RP-18e columns. The study was carried out on mother and vegetal tinctures of Passiflora incarnata L. on one single or two coupled columns. The fundamental attributions of the chromatographic profiles are evaluated using a chemometric procedure, based on the AutoCovariance Function (ACVF). Different chromatographic systems are compared in terms of their separation parameters, i.e., number of total chemical components (m_tot), separation efficiency (σ), peak capacity (n_c), overlap degree of peaks and peak purity. The obtained results show the improvements achieved by HPLC columns with narrow size particles in terms of total analysis time and chromatographic efficiency: comparable performance are achieved by Ascentis^® (2.7 μm particle) column and Acquity^® (1.7 μm particle) column requiring UPLC instruments. The ACVF plot is proposed as a simplified tool describing the chromatographic fingerprint to be used for evaluating and comparing chemical composition of plant extracts by using the parameters D% – relative abundance of the deterministic component – and c_EACF – similarity index computed on ACVF.     

Investigation of mass transfer properties and kinetic performance of high‐efficiency columns packed with C18 sub‐2 μm fully and superficially porous particles

Three columns packed with 2.0 μm superficially porous particles, 1.7 μm fully porous particles, and monodisperse 1.9 μm fully porous particles with narrow particle size distribution have been deeply characterized from a kinetic point of view. The 1.9 μm column showed excellent kinetic performance, comparable to that of the superficially porous one. These two columns also exhibit flatter c‐branches of the van Deemter curve compared to the 1.7 μm fully porous particles column, resulting in smaller loss of efficiency when they are operated at higher flow rates than the optimal ones. The independent evaluation of each contribution to band broadening has revealed that the difference in kinetic performance comes from the very small eddy dispersion contribution on the 1.9 μm column, surprisingly even lower than that of the superficially porous one. This finding suggests a very good packing of the monodisperse 1.9 μm column. On the other hand, the potential of 1.7 μm fully porous particles is completely broken down by the strong frictional heating effect already arising at relatively low flow rates.     

Formation of porous Al particles by anisotropic anodic etching

Porous Al particles were prepared by anisotropic anodic etching of small Al particles. The anisotropic anodic etching was carried out in a Cl⁻ containing electrolyte using a close-packed Al particle structure in which particles were electrically connected through the contact points between them. Anisotropic tunnel pits in the 〈100〉 direction of the Al crystal lattice were formed in the particles. After the etching, the porous Al particles could be dispersed from the close-packed structure easily. The average depth of the etching pits was ca. 25 μm. The obtained porous Al particles will be useful for various functional devices which require large surface area, such as substrates for catalysts and electrodes for electrolytic capacitors.     

Siliceous mesocellular foam for high-performance liquid chromatography: Effect of morphology and pore structure

Spherical siliceous mesocellular foam (MCF) particles with an average particle size of 4.8 μm have been successfully prepared. These spherical particles were tailored in pore sizes and surface areas. They were functionalized with C₈ or C₁₈ groups, and applied towards reversed phase high-performance liquid chromatography (HPLC) column separations. Their high surface areas gave rise to very good retention characteristics, as illustrated in the separation of a series of alkylbenzene solutes with increasing chain length. The highly interconnected porous structure and ultralarge pore size of MCF allowed the columns to be used at high flow rates without much loss in column efficiency. The column efficiency and peak symmetry were further improved by eliminating the micropores of the stationary phase. The reversed phase column packed with C₁₈-modified spherical MCF particles provided for excellent separation of different deoxynucleosides, illustrating the broad applicability of these materials due to their controlled pore size.     

Acidification and bubble template derived porous g-C3N4 for efficient photodegradation and hydrogen evolution

Graphitic carbon nitride (g-C₃N₄) as a metal-free candidate of photocatalyst has received worldwide attention because of its great potentials in solar light-induced degradation and hydrogen evolution, yet the industrial application is seriously hindered by the small specific surface area and rapid recombination rate of carriers. Herein, we demonstrate that porous g-C₃N₄ (HCl-CNU-X) can be prepared via the co-polymerization of acidified melamine and a green bubble template (urea). Transmission electron microscopy and nitrogen sorption characterization results show that the prepared HCl-CNU-X possesses an in-plane porous structure and large specific surface area, enabling the exposure of more accessible active sites. As a result, HCl-CNU-X exhibits both enhanced photocatalytic tetracycline hydrochloride degradation and higher hydrogen evolution than bulk g-C₃N₄. The boosted photocatalytic performance was ascribed to the formation of the porous structure, which dramatically promotes the separation of charge-carriers and facilitates the electron transfer. This work demonstrates that the acidification of nitrogen-rich precursors combined with a bubble-template can develop a new paradigm of highly porous photocatalysts for environmental remediation and water splitting.     

Comparison of core-shell versus fully porous particle packings for chiral liquid chromatography productivity

A loading and productivity study was done using three racemates on vancomycin and teicoplanin-bonded chiral stationary phases of different particle formats. Two columns were packed with 2.7 μm superficially porous particles and two columns were packed with identically bonded 5 μm fully porous particles. The last two columns were packed with specially synthesized 4.5 μm vancomycin and teicoplanin superficially porous particles. The loading of different chiral compounds showed that the columns filled with 2.7-μm chiral stationary phases were inappropriate for preparative separations due to their very low permeability which precluded high flow rates. However, columns containing 4.5 μm superficially porous (core-shell) particles were as effective for small-scale preparative chiral separations as columns filled with classical 5 μm fully porous particles. Comparing the 4.5 μm superficially porous particles and 5 μm fully porous particles teicoplanin columns, the observed respective productivities of 270 and 265 mg/g chiral phase/h for 5-methyl-5-phenyl hydantoin enantiomers were obtained. Particular attention was given to the peculiar case of the mianserin enantiomeric separation on vancomycin columns that gave observed productivities of 200 and 205 mg/g chiral phase/h on the 4.5 μm superficially porous particles and 5 μm fully porous particles, respectively.     

A facile bubble-assisted synthesis of porous Zn ferrite hollow microsphere and their excellent performance as an anode in lithium ion battery

Pure porous hollow Zn ferrite (ZnFe₂O₄) microspheres have been successfully synthesized by a facile bubble assisted method in the presence of ammonium acetate (NH₄Ac) as an anode material in lithium ion battery. The shape, size, and morphology of Zn ferrite are investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Furthermore, the probable bubble-assisted formation mechanism of porous hollow Zn ferrite spheres based on the experimental results is proposed. With the porous hollow structure, the obtained pure Zn ferrite particle as an anode in lithium ion battery demonstrates high capacity and excellent cycle ability. The high initial discharge specific capacity is approximately 1,400 mAh g^?1 and a reversible specific capacity approaches 584 mAh g^?1 after 100 cycles at a constant current density of 100 mA g^?1. The excellent electrochemical performance of the as-prepared Zn ferrite could be attributed to the special structure with which the volume expansion and pulverization of the particles became increasingly reduced.     

Structural characterization of hierarchically porous alumina aerogel and xerogel monoliths

Detailed nanostructures have been investigated for hierarchically porous alumina aerogels and xerogels prepared from ionic precursors via sol–gel reaction. Starting from AlCl₃·6H₂O and poly(ethylene oxide) (PEO) dissolved in a H₂O/EtOH mixed solvent, monolithic wet gels were synthesized using propylene oxide (PO) as a gelation initiator. Hierarchically porous alumina xerogels and aerogels were obtained after evaporative drying and supercritical drying, respectively. Macroporous structures are formed as a result of phase separation, while interstices between the secondary particles in the micrometer-sized gel skeletons work as mesoporous structures. Alumina xerogels exhibit considerable shrinkage during the evaporative drying process, resulting in relatively small mesopores (from 5.4 to 6.2 nm) regardless of the starting composition. For shrinkage-free alumina aerogels, on the other hand, the median mesopore size changes from 13.9 to 33.1 nm depending on the starting composition; the increases in PEO content and H₂O/EtOH volume ratio both contribute to producing smaller mesopores. Small-angle X-ray scattering (SAXS) analysis reveals that variation of median mesopore size can be ascribed to the change in agglomeration state of primary particles. As PEO content and H₂O/EtOH ratio increase, secondary particles become small, which results in relatively small mesopores. The results indicate that the agglomeration state of alumina primary particles is influenced by the presence of weakly interacting phase separation inducers such as PEO.     

The effect of diffusion on nanoaerosol filtration through porous materials with allowance for desorption processes

The effects of the finite residence time of aerosol particles in the bound state and their detachment due to thermal fluctuations on the filtration efficiency of porous and fibrous materials have been investigated with allowance for longitudinal diffusion in a flow. It has been shown that the desorption of particles affects the filtration efficiency even at times shorter than residence time τ_d of the particles in the bound state, while, at t ? τ_d, filtration stops. Allowance for the diffusion of aerosol particles in the flow leads to a decrease in the filtration efficiency as compared with the calculations performed without taking into account the longitudinal diffusion.     

Formation and performances of porous InVO4 films

Porous complex oxide films consisting of preferentially orientated orthorhombic phase of InVO₄ have been prepared using a novel simple method by pyrolysis of amorphous complex precursor. The formation and controlling of porous InVO₄ films can be easily obtained by modifying the calcination temperature. The pure orthorhombic InVO₄ phase can be obtained at a relatively lower temperature (500 °C), and the films are preferential orientation of the (200) face parallel to the substrate. The phase separation mechanism was suggested for the formation of porous films. Under visible light irradiation (λ>400 nm), porous InVO₄ films have shown the photocatalytic activity for photodegradation of gaseous formaldehyde, and can generate photocurrent. The electrochemical properties of the films with different crystal structure and pore structure were also investigated.     

Structural variation of solid core and thickness of porous shell of 1.7 μm core-shell silica particles on chromatographic performance: narrow bore columns

Chromatographic and mass transfer kinetic properties of three narrow bore columns (2.1 × 50 mm) packed with new core–shell 1.7 μm EIROSHELL™-C₁₈ (EiS-C₁₈) particles have been studied. The particles in each column varied in the solid-core to shell particle size ratio (ρ), of 0.59, 0.71 and 0.82, with a porous silica shell thickness of 350, 250 and 150 nm respectively. Scanning and transmission electron microscopy (SEM and TEM), Coulter counter analysis, gas pycnometry, nitrogen sorption analysis and inverse size exclusion chromatography (ISEC) elucidated the physical properties of these materials. The porosity measurement of the packed HILIC and C₁₈ modified phases provided the means to estimate the phase ratios of the three different shell columns (EiS-150-C₁₈, EiS-250-C₁₈ and EiS-350-C₁₈). The dependence of the chromatographic performance to the volume fraction of the porous shell was observed for all three columns. The naphtho[2,3-a]pyrene retention factor of k′ ∼ 10 on the three EiS-C_18s employed to obtain the height equivalents to theoretical plates (HETPs) data were achieved by varying the mobile phase compositions and applying the Wilke and Chang relationship to obtain a parallel reduced linear velocity. The Knox fit model gave the coefficient of the reduce HETPs for the three EiS-C_18s. The reduced plate height minimum h_min = 1.9 was achieved for the EiS-150-C₁₈ column, and generated an efficiency of over 350,000 N/m and h_min = 2.5 equivalent to an efficiency of 200,000 N/m for the EiS-350-C₁₈ column. The efficiency loss of the EiS-C18 column emanating from the system extra-column volume was discussed with respect to the porous shell thickness.     

Comparison of a new high‐resolution monolithic column with core‐shell and fully porous columns for the analysis of retinol and α‐tocopherol in human serum and breast milk by ultra‐high‐performance liquid chromatography†

The reduction of analysis time, cost, and improvement of separation efficiency are the main requirements in the development of high‐throughput assay methods in bioanalysis. It can be achieved either by ultra‐high‐performance liquid chromatography (UHPLC) using stationary phases with small particles (<2 μm) at high back pressures or by using opposite direction—monolithic stationary phases with low back pressures. The application of new types of monolithic stationary phases for UHPLC is a novel idea combining these two different paths. The aim of this work was to test the recently introduced second‐generation of monolithic column Chromolith® HighResolution for UHPLC analysis of liposoluble vitamins in comparison with core‐shell and fully porous sub‐2 μm columns with different particle sizes, column lengths, and shapes. The separation efficiency, peak shape, resolution, time of analysis, consumption of mobile phase, and lifetime of columns were calculated and compared. The main purpose of the study was to find a new, not only economical option of separation of liposoluble vitamins for routine practice.     

Adhesion of nylon particles to a quartz plate in an aqueous solution and their removal by electro-osmosis

Particle removal by electro-osmotic flow was investigated by comparison with the removal by ordinary flow of water without electrokmetic effect. The relationship between adhesion and removal of particles in terms of force acting on the particle was also discussed. Experiments were carried out in an aqueous solution using nylon particles and a quartz plate. The adhesive force,F _T, for the particles which adhered to the quartz plate in secondary minima in the total potential energy of interaction versus separation distance curves was calculated. Particle removal experiments were carried out applying electro-osmotic and Poiseuille flows. The hydrodynamic force,F _d, which was required to remove particles from the plate was estimated using flow velocities. The effectiveness of electro-osmotic flow on particle removal was larger than that of Poiseuille flow. In the particle removal by electro-osmotic flow, the minimum of the ratioF _d/F _t for particle removal was found to be 50 and the ratio for removal efficiency of 0.5 was about 140.     

Porosity of porous Al alloys

Two porosity models of porous Al alloys with different pore types (ball and polygon shape) were established. The experimental results coincide well with theoretical computations. The porosity of Al alloys (Pr _c) consists of three parts, porosity caused by preform particles (Pr _p), additional porosity (Pr _a), and porosity caused by solidification shrinkage (Pr _s).Pr _pis the main part ofPr _c whilePr _a is the key for fabricating porous Al alloys successfully in spite of its little contribution toPr _c.     

Cu cluster embedded porous nanofibers for high-performance CO2 electroreduction

Metal-doped carbon materials, as one of the most important electrocatalytic catalysts for CO₂ reduction reaction (CO₂RR), have attracted increasing attention. Herein, a series of Cu cluster embedded highly porous nanofibers have been prepared through the carbonization of electro-spun MOF/PAN nanofibers. The obtained Cu cluster doped porous nanofibers possessed fibrous morphology, high porosity, conductivity, and uniformly dispersed Cu clusters, which could be applied as promising CO₂RR catalysts. Specifically, best of them, MCP-500 exhibited high catalytic performance for CO₂RR, in which the Faradaic efficiency of CO (FE_CO) was as high as 98% at ?0.8 V and maintained above 95% after 10 h continuous electrocatalysis. The high performance might be attributed to the synergistic effect of tremendously layered graphene skeleton and uniformly dispersed Cu clusters that could largely promote the electron conductivity, mass transfer and catalytic activity during the electrocatalytic CO₂RR process. This attempt will provide a new idea to design highly active CO₂RR electrocatalyst.