Method of Discrimination of Surface Fractality

Abstract A simple method for the discrimination of surface fractality is proposed. This method is based on the comparison of the nitrogen adsorption isotherm on a given sample with the "standard" isotherm on a smooth surface. The proposed comparative method makes it possible to determine the lower limit of the scale range of surface fractality. A thermodynamic method is recommended as a complement to fractal analysis in the scale range of about 10-1000 A. The results of the investigation of surface roughness are presented with examples of typical samples of silica gels, porous glasses, apatite, and coal.

Micellar electrokinetic capillary chromatography for therapeutic drug monitoring of carbamazepine and its main metabolites.

In carbamazepine (CBZ) therapy the concomitant monitoring of concentrations of CBZ and its metabolites is strictly recommended, primarily to avoid toxic side effects. Currently, clinical routine monitoring of CBZ is accomplished by high-performance liquid chromatography or immunological methods. In this study a micellar electrokinetic capillary chromatographic (MECC) method was developed for routine drug monitoring of CBZ and its main metabolites, carbamazepine 10,11-diol and carbamazepine 10,11-epoxide, in human serum or plasma samples. The MECC method enabled baseline separation of all analytes within 2.5 min. The assay revealed sufficient precision and sensitivity and the results of eith…

Chromatography. A Science of Discovery. Herausgegeben von Robert L. Wixom und Charles W. Gehrke.

Chromatography. A Science of Discovery. Edited by Robert L. Wixom and Charles W. Gehrke.

Analytical technique for studying the structure of glycoprotein N-glycans

Abstract The aim of this study was to develop an analytical strategy for the structural analysis of glycoprotein N-glycans by combining several sensitive methods without any elaborate equipment. The following consecutive steps were optimized and applied: (1) immobilization of glycopeptide N-glycosidase F (EC 3.2.2.18) on several polymeric and a silica support, the latter giving a maximum binding capacity of 11.3% of starting activity; (2) lectin affinity chromatography was miniaturized using Mobitec columns of volume 200 μl; the binding capacity of glycoproteins on concanavalin A and wheat germ agglutinin columns was in the range 0.5–1 μg; (3) N-linked oligosaccharides were isolated from co…

Surfactant controlled preparation of mesostructured transition-metal oxide compounds

The use of surfactants as templates allows the synthesis of mesostructured transition-metal oxides by a cooperative, interface controlled condensation process.

Making Broad Proteome Protein Measurements in 1−5 min Using High-Speed RPLC Separations and High-Accuracy Mass Measurements

The throughput of proteomics measurements that provide broad protein coverage is limited by the quality and speed of both the separations as well as the subsequent mass spectrometric analysis; at present, analysis times can range anywhere from hours (high throughput) to days or longer (low throughput). We have explored the basis for proteomics analyses conducted on the order of minutes using high-speed capillary RPLC combined through on-line electrospray ionization interface with high-accuracy mass spectrometry (MS) measurements. Short 0.8-microm porous C18 particle-packed 50-microm-i.d. capillaries were used to speed the RPLC separations while still providing high-quality separations. Both…

Agglomerated non-porous silica nanoparticles as model carriers in polyethylene synthesis

Abstract Non-porous submicron silica particles (250 and 500 nm) with high monodispersity were agglomerated to form spherical agglomerates via spray drying. As a binder, 25 nm sized monodisperse silica spheres were selected from a variety of colloidal systems including Levasil-type and Aerosil-type silica nanoparticles. The use of such binders led to an increase of the specific surface area of the agglomerated carriers. All materials were characterised by nitrogen sorption, mercury intrusion and scanning electron microscopy. The silica agglomerates, with highly defined geometrical and pore structural parameters, were employed as model carriers in the heterogeneous polymerization of ethylene …

Metal Oxide Containing Mesoporous Silica with Bicontinuous “Plumber's Nightmare” Morphology from a Block Copolymer-Hybrid Mesophase

Isolation and Characterization of Structurally Novel Antimutagenic Flavonoids from Spinach (Spinacia oleracea)

Thirteen compounds, isolated from spinach (Spinacia oleracea), acted as antimutagens against the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline in Salmonella typhimurium TA 98. The antimutagens were purified by preparative and micropreparative HPLC from a methanol/water (70:30, v/v) extract of dry spinach (commercial product) after removal of lipophilic compounds such as chlorophylls and carotenoids by solid-phase extraction (SPE). Pure active compounds were identified by instrumental analysis including FT-IR, (1)H and (13)C NMR, UV-vis spectroscopy, and mass spectrometry. All of these compounds were flavonoids and related compounds that could be attributed to five groups: (A, m…

Pore structural characteristics, size exclusion properties and column performance of two mesoporous amorphous silicas and their pseudomorphically transformed MCM-41 type derivatives

Highly ordered mesoporous silicas such as, mobile composition of matter, MCM-41, MCM-48, and the SBA-types of materials have helped to a large extent to understand the formation mechanisms of the pore structure of adsorbents and to improve the methods of pore structural characterization. It still remains an open question whether the high order, the regularity of the pore system, and the narrow pore size distribution of the materials will lead to a substantial benefit when these materials are employed in liquid phase separation processes. MCM-41 type 10 microm beads are synthesized following the route of pseudomorphic transformation of highly porous amorphous silicas. Highly porous silicas a…

Profiling of endogenous peptides by multidimensional liquid chromatography: On-line automated sample cleanup for biomarker discovery in human urine.

A simple and flexible system, employing a column switching technique, has been designed to allow the analysis of peptides and proteins smaller than 15 kDa by molecular weight in filtered urine samples by performing a direct on-column injection utilising simultaneous sample clean-up and trace enrichment. The positively charged peptides and small proteins in the sample are attracted to the inner, negatively charged pore structure of the RAM-SCX column while the larger proteins and uncharged or negatively charged compounds are excluded. After preconditioning with the biological sample, large amounts of sample can be injected. Several important and adjustable parameters for the proper use of a …

Pore structural characterization of monolithic silica columns by inverse size-exclusion chromatography

In this work, a parallel pore model (PPM) and a pore network model (PNM) are developed to provide a state-of-art method for the calculation of several characteristic pore structural parameters from inverse size-exclusion chromatography (ISEC) experiments. The proposed PPM and PNM could be applicable to both monoliths and columns packed with porous particles. The PPM and PNM proposed in this work are able to predict the existence of the second inflection point in the experimental exclusion curve that has been observed for monolithic materials by accounting for volume partitioning of the polymer standards in the macropores of the column. The appearance and prominence of the second inflection …

Dry synthesis of B-MFI, MTN- and MTW-type materials

Abstract B-MFI and MTN-type materials were synthesized via the fluoride route from dry powders in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO 2 · Al 2 O 3 gels at 700°C were transformed into MTN-type material in the presence of dried NH 4 F and TMACl. Amorphous precursors obtained by drying SiO 2 gels at 700°C were transformed into B-MFI in the presence of dried NH 4 F, B 2 O 3 and TPABr. Water is formed as a reaction product. However, the water vapor pressure is appreciably below the water vapor saturation pressure under the given reaction conditions. In addition, syntheses using seed crystals were carried out successfully.

Selectivity tuning in pressurized-flow electrochromatography

Abstract Pressurized-flow electrochromatography (PEC) is a developing separation technique in which both a pressure gradient and an electric field are applied across a packed capillary. In this work we present new results illustrating the principles and the potential of PEC. Home-made capillary columns with silica-based reversed phase packings were operated under PEC conditions separating low molecular weight analytes. Compared to the purely pressure-driven system enhanced selectivity for the charged analytes was observed. It is shown that the retention time of a retained cationic analyte in PEC can be calculated using the chromatographic capacity factor and the electrophoretic mobility of …

Peptide mapping by reversed-phase high-performance liquid chromatography employing silica rod monoliths.

In this paper, a general procedure is described for the generation of peptide maps of proteins with monolithic silica-based columns. The peptide fragments were obtained by tryptic digestion of various cytochrome c species with purification of the tryptic fragments achieved by reversed-phase high-performance liquid chromatographic methods. Peak assignment of the various peptides was based on evaluation of the biophysical properties of the individual peptides and via mass spectrometric identification. The performance of several different monolithic sorbents prepared as columns of identical cross-sectional dimensions were investigated as part of these peptide mapping studies and the data evalu…

ChemInform Abstract: Liquid Chromatography - Its Development and Key Role in Life Science Applications

Liquid chromatographic methods cover the broadest range of appli- cations imaginable today. Nowhere is this more evident and relevant than in the life sciences, where identification of target substances relevant in disease mechanisms is performed down to the femtomole level. On the other hand, purification of therapeutic drugs on a multi- ton scale is performed by process LC. The complexity and abundance range of biological systems in combination with the extreme purity requirements for drug manufacturing are the challenges that can be mastered today by chromatography, after more than a century of research and development. However, significant improvement is still required for a better unde…

Silica gel chemistry

Automated multi-dimensional liquid chromatography

A comprehensive on-line sample clean-up with an integrated two-dimensional HPLC system was developed for the analysis of natural peptides. Samples comprised of endogenous peptides with molecular weights up to 20 kDa were generated from human hemofiltrate (HF) obtained from patients with chronic renal failure. The (poly-)peptides were separated using novel silica-based restricted access materials with strong cation-exchange functionalities (SCX-RAM). The size-selective sample fractionation step is followed by cation-exchange chromatography as the first dimension. The subsequent second dimension of separation is based on hydrophobic interaction using four parallel short reversed-phase (RP) co…

Capillary electroendoosmotic chromatography of peptides

This review focuses on the current state of peptide separation by capillary electroendoosmotic chromatography (CEC). When carried out under optimised conditions, peptide separation by CEC methods represents an orthogonal and complementary technique to micro-HPLC (micro-HPLC) and high-performance capillary zone electrophoresis (HPCZE). The origin of the selectivity differences that can be achieved with these three separation techniques (CEC, micro-HPLC and HPCZE), respectively are discussed, and the current limits of performance with CEC methods documented. Peptide separations by CEC methods with n-alkyl bonded silicas or mixed-mode phases are also illustrated. The development of different v…

Optimization of the phase system in the analysis of polynuclear aromatics (PNA) from diesel engine exhaust by high performance liquid chromatography (HPLC)

Polynuclear aromatics (PNA) were collected and enriched from diesel engine exhausts by means of a probe and an absorber system. Group separation of PNA from other constituents of exhaust was accomplished through elution with n-heptane on a silica column. A variety of phase systems ranging from unpolar to strong polar packings and eluents, respectively, were tested to resolve PNA into single species. Of these a n-octadecyl bonded silica packing and methanol/water was found to be the most optimal with regard to resolution for real PNA mixtures. Separation was completed within 2–3 h at isocratic conditions.

Comprehensive pore structure characterization of silica monoliths with controlled mesopore size and macropore size by nitrogen sorption, mercury porosimetry, transmission electron microscopy and inverse size exclusion chromatography

The porosity of monolithic silica columns is measured by using different analytical methods. Two sets of monoliths were prepared with a given mesopore diameter of 10 and 25 nm, respectively and with gradated macropore diameters between 1.8 and 7.5 microm. After preparing the two sets of monolithic silica columns with different macro- and mesopores the internal, external and total porosity of these columns are determined by inverse size-exclusion chromatography (ISEC) using polystyrene samples of narrow molecular size distribution and known average molecular weight. The ISEC data from the 4.6 mm analytical monolithic silica columns are used to determine the structural properties of monolithi…

Comparative study of capillary electroendosmotic chromatography and electrically assisted gradient nano-liquid chromatography for the separation of peptides.

Capillary electroendoendosmotic chromatography (CEC), being a hybrid of high-performance liquid chromatography (HPLC) and capillary electrophoresis, offers considerable changes to enhance column efficiency, speed of analysis and additional selectivity as compared to the parent methods. The analytes are driven by the electroendosmotic flow (EOF) and separated by surface-solute interactions as well as by differences in electromigration. In this paper on the separation of peptides on C18 reversed-phase and mixed-mode (sulphonic acid-n-alkyl) packings in CEC and electrically assisted reversed-phase gradient nano-LC are investigated. It is shown that mixed mode packings generate a higher EOF tha…

Untersuchungen zur Herstellung von ZSM-5-Schalen- und Vollkatalysatoren

Factors affecting the UV-Transparency of Molecular Sieves

The optical properties in the UV-region of several types of molecular sieves were studied. The initial onset of absorption around 280 nm which was observed for basically all samles synthesized without special precautions is not due to an early onset of band gap absorption, but might be correlated to the crystal size as well as structural defects within the crystals, e.g. E'-center or peroxy-radical. Using template free synthesis procedures which lead to small crystals containing few defect sites, we were able to synthesize molevular sieves which were almost completely transparent down to 200 nm. Such crystals can become very important in the development of technical luminophores.

Formation of a Porous Zirconium Oxo Phosphate with a High Surface Area by a Surfactant-Assisted Synthesis

Sorption Kinetics of Benzene and p-Xylene on Template Supported Synthesized Gallosilicates

Adsorption equilibria and kinetics of benzene and p-xylene on microporous gallosilicates (Ga-MFI) were measured piezometrically to ascertain the role of Ga in the system and to compare it with Ga-free MFI structures. The intracrystalline mobility of benzene follows a diffusional mechanism throughout the entire concentration range with an energy of activation that considerably exceeds that for the Ga-free species (78 kJmol−1 and 26 kJmol−1, respectively). For p-xylene, the kinetics indicate the existence of three sorption states. Sorbing species become highly immobile at a pore filling of ca n > 4 molecules per unit cell, i.e. in the range of concentration where isotherm hysteresis occurs. T…

Untersuchungen zum Agglomerationsmechanismus bei der Herstellung von extrudierbaren Tonerdepasten

Ultrahigh-Throughput Proteomics Using Fast RPLC Separations with ESI-MS/MS

We describe approaches for proteomics analysis using electrospray ionization-tandem mass spectrometry coupled with fast reversed-phase liquid chromatography (RPLC) separations. The RPLC separations used 50-microm-i.d. fused-silica capillaries packed with submicrometer-sized C18-bonded porous silica particles and achieved peak capacities of 130-420 for analytes from proteome tryptic digests. When these separations were combined with linear ion trap tandem mass spectrometry measurements, approximately 1000 proteins could be identified in 50 min from approximately 4000 identified tryptic peptides; approximately 550 proteins in 20 min from approximately 1800 peptides; and approximately 250 prot…

CATALYTIC OXIDE COATINGS ON CERAMIC SUPPORTS.

Thin porous oxide coatings composed of Al2O3, SiO2, TiO2 and ZrO2, respectively, on ceramic carriers have been produced by either a wash-coat procedure or by liquid coating followed by solidification. By dehydration and calcination of the supported ceramics the pore texture was stabilised. The thickness of the layer, its homogeneity, specific surface area, porosity and pore volume distribution have been shown to be controlled by the properties of the oxides deposited, and by the conditions of the coating procedures. On the basis of the results obtained, it is evident that porous oxide layers can be prepared with tailor-made and desired properties. The procedures described also permit the in…

Monolithic silica columns of various format in automated sample clean-up/multidimensional liquid chromatography/mass spectrometry for peptidomics.

The following particulate and monolithic silica columns were implemented in a fully automated and flexible multidimensional LC/MS system with integrated sample clean-up, to perform the analysis of endogeneous peptides from filtered urine and plasma samples: restricted access sulphonic acid strong cation-exchanger (RAM-SCX) for sample clean-up, RP 18 Chromolith guard columns as trap columns and 100 microm I.D. monolithic RP 18 fused silica capillary columns as last LC dimension. The results show sufficient overall system reproducibility and repeatability. Implementation of monolithic silica columns added an additional flexibility with respect to flow rate variation and adjustment due to the …

Capillary electrochromatography analysis of hormonal cyclic and linear peptides.

The retention behavior of linear and cyclic peptides has been studied by capillary electrochromatography (CEC) with a variety of different n-alkyl silica reversed-phase sorbents and also with mixed-mode phases containing both strong cation-exchange (sulfonic acid) and n-alkyl groups bonded onto the silica surface, using eluents ranging from pH 2.0 to pH 5.0. Depending upon the amino acid sequence, electrochromatographic retention of the peptides was strongly affected by the composition of the eluent, its pH value, and the choice of sorbent packed into the capillaries. The dominant separation processes operating with these charged analytes could be modulated inter alia by the content of orga…

ChemInform Abstract: The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework.

Chromatography

Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatography

Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (approximately 1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the microme…

Ein poröses Zirconiumoxophosphat sehr hoher Oberfläche durch eine tensidunterstützte Synthese

Calculation of the molecular masses of two newly synthesized thermostable enzymes isolated from thermophilic microorganisms

Two thermostable enzymes synthesized by thermophilic microorganisms were isolated and purified. A thermostable beta-galactosidase was produced in a continuous fermentation process by Bacillus stearothermophilus TP 32 as an intracellular enzyme. After applying different concentration procedures the raw extract enzyme was prepurified on a Sephadex G-200 size exclusion column. The isolated beta-galactosidase fraction was then separated with HPLC on a TSK G 3000 SW size exclusion column to determine the molecular mass based on calibration curves of standard proteins. The other enzyme, a thermostable protease, was synthesized by Bacillus stearothermophilus TP 26 as an extracellular enzyme. After…

Rotational State Change of Acetonitrile Vapor on MCM-41 upon Capillary Condensation with the aid of Time-Correlation Function Analysis of IR Spectroscopy

The infrared spectra of adsorbed acetonitrile on MCM-41 (porewidth = 3.2 nm) were measured at 303 K. In the CN stretching ν2 region, two bands were observed at 2265 cm− 1 and 2254 cm− 1, assigned to hydrogen-bonded molecules on surface hydroxyls of MCM-41, and physisorbed molecules in mesopores, respectively. We designate here the 2265 cm− 1 band as the ν2α band and the 2254 cm− 1 band as the ν2β band. The bandwidth of the fundamental transition ν2fβ, was obtained by removing the overlap with hot band transitions of the same mode, ν2α band, and other modes by least-squares fitting. Before capillary condensation, the relaxation time τ obtained from the bandwidth of the ν2fβ band was smaller …

Consecutive Selective Adsorption of Pentamidine and Phosphate Biomolecules on a Self-Assembled Layer:  Reversible Formation of a Chemically Selective Coating

In situ ellipsometric film thickness measurements, FT-IR external reflectance spectroscopy, and potentiometric measurements indicated that the amphiphile pentamidine (PAM), a bisbenzamidine, associated by self-assembly with a preformed self-assembled monolayer of a mercaptoalkanoic acid on gold. The structural properties of PAM and the nature of the substrate were ideal for the formation of a densely packed monolayer. This process was fully reversible, as demonstrated by changing the pH of the surrounding medium. Thus, disassembly−reassembly occurred when the pH was cycled between 8.7 and 3. The bilayer structure, featuring a positively charged amidinium surface, was subsequently used for s…

Controlling the spatial distribution of aluminum in ZSM-5 crystals

Abstract The spatial distribution of aluminum over ZSM-5 crystals was systematically studied using electron microprobing on polished crystals. Crystals synthesized with TPABr as template exhibit a pronounced enrichment of aluminum in the crystal rim, essentially irrespective of the aluminum source employed, although aluminum sources with organic anions are favoring less inhomogeneous profiles. With 1,6-hexanediol or from totally inorganic reaction gels, crystals with completely homogeneous aluminum profiles are obtained, even if the crystals grow larger than 50 μm. In the 1,6-hexanediol system the homogeneous profiles could be changed to profiles similar to the TPABr system by addition of K…

A critical appraisal of capillary electrochromatography.

Although still in its infancy, CEC promises some advantages over competitive techniques for separating charged analytes including biomolecules.

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

The targeted optimization of the functional properties of porous materials includes the understanding of their transport properties and thus requires knowledge about the relationship between material synthesis, resulting in three-dimensional material morphology, and relevant transport properties. In this Perspective, we present our views and results on the characterization of microscopic disorder in functional porous materials, which are widely used today as fixed beds in adsorption, separation, and catalysis. This allows us to identify structural parameters that impact their mass transport properties and eventually their overall performance in technological operations. We address this comp…

A strategy for chromatographic and structural analysis of monosaccharide species from glycoproteins.

A general strategy for the chromatographic and structural analysis of the monosaccharide species fucose (Fuc), N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), galactose (Gal), glucose (Glc), mannose (Man), N-acetylneuraminic acid (NANA) present in glycoproteins is described. Qualitative and quantitative aspects for the separation of these glycoprotein monosaccharides (monosaccharide species) using ligand-exchange chromatography (LEC) and high pH anion-exchange chromatography (HPAEC) in combination with pulsed-amperometric detection (PAD), refractive index (RI) and ultraviolet (UV) monitoring are discussed in detail. The conditions for the acidic hydrolysis of glycoproteins and…

Adsorbents and columns in analytical high-performance liquid chromatography: A perspective with regard to development and understanding

A brief historical survey is presented on the evaluation of silica adsorbents in analytical HPLC. The theory of analytical HPLC is mostly still being based on the height equivalent to a theoretical plate concept and the van Deemter equation that was derived from gas phase adsorption involving a linear adsorption isotherm and fast mass transfer kinetics. One can obviously wonder whether the use of the van Deemter equation is relevant and valid for the evaluation of the performance of HPLC systems, where most often the liquid solutes involve charged molecules in electrolytes and in very many cases the adsorbates are macromolecules having diffusion coefficients of small magnitude. Instead of t…

Polymer-coated reversed-phase packings with controlled hydrophobic properties

Abstract We have designed and synthesized novel reversed-phase packings of non-porous and porous polymethacrylate-coated silicas. By varying the hydrophobicity of the polymer coating, selective unfolding of polypeptides may be achieved, thus enabling manipulation of the chromatographic profile. This study characterizes these packings through their employment for separations of model synthetic peptides of defined secondary, tertiary and quaternary structure. Thus, the packings were applied to the reversed-phase separation α-helical amphipathic and non-amphipathic peptides of the same amino acid composition but different sequences. In addition, selective unfolding of model to-stranded α-helic…

Synthetische Zeolithe und Aluminophosphate

The synthesis of micrometer- and submicrometer-size spheres of ordered mesoporous oxide MCM-41

Column technology in liquid chromatography

This chapter deals with the most important part of the liquid chromatography (LC) system: the column enabling the efficient and fast resolution of complex mixtures. It is divided into seven sections under the overall aspects of manufacture, operation, and evaluation of analytical columns for the user. The first three sections highlight the column design and hardware, followed by a thorough treatment of the properties of microparticulate silica adsorbents as packing material, stationary phases performed by surface functionalization, and the column filling process. Then, the implementation of the column into the LC system is discussed, leading into chromatographic column testing as a C18-bond…

Novel pathways for the preparation of mesoporous MCM-41 materials: control of porosity and morphology

Two novel synthesis routes for the preparation of mesoporous MCM-41 materials are introduced. Both methods use tetra-n-alkoxysilanes such as tetraethoxysilane (TEOS) or tetra-n-propoxysilane (TPS) as a silica source which are added to an aqueous solution of a cationic surfactant in the presence of ammonia as catalyst. In this study, n-alkyltrimethylammonium bromides and n-alkylpyridinium chlorides were employed as templates. The addition of an alcohol (e.g. ethanol or isopropanol) leads to a homogeneous system which allows the formation of spherical MCM-41 particles. The main advantages of these methods are short reaction times, excellent reproducibility and easy preparation of large batche…

Liquid chromatography--its development and key role in life science applications.

Liquid chromatographic methods cover the broadest range of appli- cations imaginable today. Nowhere is this more evident and relevant than in the life sciences, where identification of target substances relevant in disease mechanisms is performed down to the femtomole level. On the other hand, purification of therapeutic drugs on a multi- ton scale is performed by process LC. The complexity and abundance range of biological systems in combination with the extreme purity requirements for drug manufacturing are the challenges that can be mastered today by chromatography, after more than a century of research and development. However, significant improvement is still required for a better unde…

Molecular mechanism of capillary condensation of acetonitrile vapor on MCM-41 with the aid of a time-correlation function analysis of IR spectroscopy

Abstract The adsorption isotherm and IR spectra of acetonitrile adsorbed on MCM-41 (pore-width=3.2 nm) were measured at 303 K. The adsorption isotherm had a sharp jump at P / P 0 =0.3 without adsorption hysteresis. The CN stretching ν 2 -band of adsorbed acetonitrile had two-component α- and β-bands at 2263 and 2254 cm −1 , respectively, assigned to hydrogen-bonded molecules on surface hydroxyls of MCM-41 and physisorbed molecules in mesopores whose walls are coated with hydrogen-bonded molecules, respectively. The β-band was analyzed with a time correlation function, giving a reorientation time τ . The τ value of the adsorbed molecule before capillary condensation was smaller than that of …

Bioanalysis of digoxin and its metabolites using direct serum injection combined with liquid chromatography and on-line immunochemical detection.

Abstract An automated dual-column liquid chromatographic assay for digoxin is described. Serum samples are directly injected onto a restricted-access solid-phase extraction support. After liquid chromatographic (LC) separation on a C18 analytical column, antigenic analytes are detected by means of post-column immunochemical detection (ICD) using fluorescein-labelled antibodies against digoxigenin. The detection limit of this assay is 160 pg/ml (preconcentration of 1.0 ml serum). With the present method digoxin and three of its cross-reactive metabolites were determined in serum taken from patients which were orally administered a 1-mg dose of digoxin. The results obtained with LC—ICD were c…

Structural selectivity provided by starburst dendrimers as pseudostationary phase in electrokinetic chromatography

Abstract Starburst dendrimers (SBDs) were used as a pseudostationary phase in electrokinetic chromatography (EKC) of hydrophobic compounds. The selectivity of SBD-mediated EKC (SBD-EKC) was different from those in micellar EKC (MEKC) systems, in spite of the apparent structural resemblance between micelles and SBDs. The SBDs provided similar selectivity as polymer gel packing materials in reversed-phase liquid chromatography (RPLC), showing little selectivity for alkyl groups and clear preference for aromatic compounds, especially for rigid, planar polynuclear aromatic hydrocarbons. The alkylation of SBDs resulted in the increased retention and hydrophobic selectivity while maintaining the …

Towards the column bed stabilization of columns in capillary electroendosmotic chromatography

This article discusses a novel method generating a continuous bed inside the CEC column. The column bed composed of microparticulate reversed-phase silica is completely immobilized by a hydrothermal treatment using water for the immobilization process. This process eliminates the manufacture of frits of both ends of the column and all problems associated with their preparation. Fundamental studies on operational parameters will be presented such as the dependence of the immobilization on the column temperature, the type of stationary phase and the column back pressure. The immobilized CEC columns show the same high column efficiency as packed columns with frits.

High-resolution physisorption techniques for the characterization of adsorbents and catalysts

Abstract High-resolution physisorption techniques performed in the continuous volumetric mode have been developed to investigate the surface and pore structure properties of porous solids. Physisorption data on well-defined microporous solids (zeolites and aluminophosphates) provide novel information on the mechanism of micropore filling, the behavior of the adsorbed phase and the pore structure of the adsorbent. The combination of physisorption with high-resolution analytical techniques such as calorimetry and neutron diffraction further expands our knowledge and understanding of physisorption processes. The results are not only important for fundamental research but can be applied in the …

Grafting of Molecularly Imprinted Polymer Films on Silica Supports Containing Surface-Bound Free Radical Initiators

Silica particles containing surface-bound free radical initiators have been used as supports for the grafting of thin films of molecularly imprinted polymers (MIPs). This technique offers a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity in chromatographic or sensor applications. Thus prepared MIPs imprinted with l-phenylalanine anilide, have been characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis, fluorescence microscopy, and scanning electron microscopy (SEM), providing evidence concerning the reproducibility in each step and the quantity and quality of the grafted…

Polymer support synthesis

Non-porous silica gel microbeads of diameter 1.5 microns have been investigated as supports for oligonucleotide synthesis. In the preparation of oligothymidylates of chain length up to 150 bases, with 5'-di-p-anisylphenylmethyl-3'-phosphoramidite as an intermediate, the average yields per chain elongation were up to 99%. Lower overall yields were observed in the case of a support which developed a strong tendency towards aggregation after the build up of an oligonucleotide coating.

Life-time studies with capillary electrochromatography columns operated under different conditions.

A test system has been established to permit the monitoring of the life-time performance of several reversed- phase capillary electrochromatography (CEC) columns. The retention factors, k(cec), peak symmetry coefficients, lambda(sym), and column efficiencies, N, of three neutral n-alkylbenzene analytes, namely ethyl-, n-butyl- and n-pentylbenzenes, were determined for Hypersil 3 microm n-octylsilica and n-octadecylsilica packed into CEC capillary columns of 100 microm I.D., with a packed length of 250 mm, and a total length of 335 mm. The performances of these CEC capillary columns were examined for a variety of eluents with pH values ranging between pH 2.0 - 8.0, similar to those employed …

An automated on-line multidimensional HPLC system for protein and peptide mapping with integrated sample preparation.

A comprehensive on-line two-dimensional 2D-HPLC system with integrated sample preparation was developed for the analysis of proteins and peptides with a molecular weight below 20 kDa. The system setup provided fast separations and high resolving power and is considered to be a complementary technique to 2D gel electrophoresis in proteomics. The on-line system reproducibly resolved approximately 1000 peaks within the total analysis time of 96 min and avoided sample losses by off-line sample handling. The low-molecular-weight target analytes were separated from the matrix using novel silica-based restricted access materials (RAM) with ion exchange functionalities. The size-selective sample fr…

Multidimensional Column Liquid Chromatography (LC) in Proteomics – Where Are We Now?

MCM-41, MCM-48 and related mesoporous adsorbents: their synthesis and characterisation

MCM-41, MCM-48, MCM-41 analogue materials and disordered silica xerogels were compared with respect to their long range and short range order, their specific surface area, pore structure and pore structural parameters, pore wall thickness and their surface hydroxyl group concentration. Based on X-ray diffraction data it could be seen that the degree of long range order decreased in the order MCM-41>MCM-48>MCM-41 analogues >amorphous silica xerogels. The particle porosity and pore wall thickness increased in the same sequence such that MCM-41 analogues and amorphous silica xerogels were more stable towards water and water vapour. The concentration of the surface hydroxyl groups increased whe…

Polymer-coated reversed-phase packings in high-performance liquid chromatography

The synthesis and properties of polymer-coated RP stationary phases are reviewed. The sorbents are classified according to the method of synthesis. More flexibility in the tailoring of polymer-coated packings is noted. The impact of the polymer coating on the porosity of the oxides to be modified and their chromatographic properties is discussed.

Flüssigkeitschromatographie - ihre Entwicklung und Bedeutung für die Lebenswissenschaften

Flussigkeitschromatographische Methoden umfassen den breitest heute vorstellbaren Anwendungsbereich. Dies wird nirgendwo so deutlich wie in den Lebenswissenschaften, wenn es darum geht, Krankheitsmechanismen aufzuklaren und komplexe Gemische bis in den Femtomol-Bereich zu analysieren. Auf der anderen Seite besteht Bedarf an hochreinen therapeutischen Wirkstoffen, die als Pharmaka auf den Markt kommen und hohen Reinheitsanforderungen genugen mussen. Diese Aufreinigung wird mithilfe der Prozesschromatographie im Tonnenmasstab bewerkstelligt. Die hohe Komplexitat und breiten Konzentrationsbereiche biologischer Systeme in Kombination mit den extremen Reinheitsanforderungen der Arzneimittelprodu…

Anthraquinones formation on zeolites with BEA structure

Publisher Summary Zeolites with BEA structure are in focus mainly in the field of conversion of hydrocarbons. However, their unique physico-chemical properties let to suppose that these systems can be successfully used in reactions of organic synthesis. Such zeolites can be used as catalysts for the synthesis of large organic molecules. The interaction of phthalic anhydride with aromatic hydrocarbons is a subject for investigation, both for science purposes and for industrial applications. The use of zeolites in this reaction is an example of the acylation of aromatics on solid-acid catalysts; on the other hand, such a study creates the possibilities of developing more appropriate technolog…

A Novel Pathway for Synthesis of Submicrometer-Size Solid Core/Mesoporous Shell Silica Spheres

MCM-41 and related materials as media for controlled polymerization processes

The synthesis of mesoporous MCM-41 type materials based on transition metal oxides and the polymerization of several monomers within MCM-41 is presented with the aim to specifically investigate the effects of the interface and confinement on host-guest interactions. In addition to standard MCM-41, material based on transition metal oxides is obtained although template removal has been unsuccessful for such compounds until now. In situ polymerization of styrene, methyl methacrylate and vinyl acetate is possible within the mesopore system. The properties of some of the encapsulated polymers differ markedly with those obtained in the bulk.

Interactions of lysozyme with hydrophilic and hydrophobic polymethacrylate stationary phases in reversed phase chromatography (RPC)

Two silicas, one with a mean pore diameter of 30 nm and the other non-porous, were coated with polymethacrylates of increasing hydrophobicity in the sequence: poly-2-hydroxyethylmethacrylate (P2HEMA)1 polyethylmethacrylate (PEMA) and poly-n-octylmethacrylate (POMA). Association constants, Kass, between lysozyme and the coated silicas were determined by means of frontal analysis, and the apparent heats of adsorption, delta Happ, by means of microcalorimetry. Using Kass and delta Happ the changes in the apparent free energy, delta Gapp, and in the apparent entropy, delta Sapp, were calculated at a concentration of lysozyme < 10 mumol/l. The association between the lysozyme and the coated sili…

Characterization of the Pore Structure of Monolithic Silicas

Spherical silica agglomerates possessing hierarchical porosity prepared by spray drying of MCM-41 and MCM-48 nanospheres

Hierarchically ordered porous materials possessing both meso- and macropores can be obtained by agglomeration of spherical primary particles of mesoporous MCM-41 and MCM-48 materials using the spray drying technique. A highly interconnected bimodal pore network is obtained due to the intra- and inter-particle pore systems within the micron-sized spherical agglomerates. Further packing of the agglomerates will result in a three-modal hierarchical pore system, where the first level of porosity originates from the ordered mesopores inside the primary particles, the second level is a result of the particle internal porosity, and the third level is due to the voids between the agglomerates. The …

Is the formation of a zeolite from a dry powder via a gas phase transport process possible?

Abstract ZSM-5 was synthesized by four methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in the form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO2·A2O3 gels at 650°C were transformed into zeolites in the presence of dried NH4F and TPABr. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure under the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF4 as the mobile species between the solid phase, which contains the amorphous Si/Al pre…

Application of CEC procedures for the analysis of synthetic peptides: characterization of linear immunogenic peptides that mimic a HIV-1 gp120 epitope

In this study, we describe the application of a new analytical procedure based on capillary electrochromatographic(CEC) techniques for the characterization of different basic and acidic peptides using isocratic eluent conditions containing acetonitrile and ammonium acetate buffers of different molarities between pH 3.8 and 5.2. In particular,10 immunogenic peptide analogs with isoelectric points ranging from 3.7 to 10.1 were investigated; nine of these peptides, 1-9, were truncated analogs of the parent peptide, 10, which is a peptidomimetic related to a HIV-1 gp120 epitope. Several of these peptides have the propensity to form alpha-helical secondary structures in solution. Electrochromato…

Pressurized flow electrochromatography with reversed phase capillary columns

Pressurized flow electrochromatography (PEC) is a hybrid of capillary LC and capillary electroendosmotic chromatography (CEC). Both a pressure gradient and an electric field are applied across a packed capillary. The feasability of a simple, easy to handle PEC instrumentation is demonstrated. Home made capillary columns with four different silica-based reversed phase packings have been operated under PEC conditions separating non ionic and ionic low molecular weight analytes. The capillary columns have been characterized with respect to their separation efficiency and selectivity and the results have been compared to those obtained with the purely pressure driven system. An electrochromatog…

Proteolytic cleavage of soybean Bowman-Birk inhibitor monitored by means of high-performance capillary electrophoresis. Implications for the mechanism of proteinase inhibitors

The hydrolysis of the soybean Bowman-Birk inhibitor in the presence of catalytic amounts of bovine trypsin and the formation of the non-covalent enzyme-inhibitor complex with an equimolar amount of enzyme are monitored by means of high-performance capillary electrophoresis (HPCE). The inhibitor is cleaved in the trypsin-reactive and more slowly in the chymotrypsin-reactive subdomain. HPCE proves itself as the only reliable analytical tool to monitor these reactions in clear contrast to classical electrophoretic, chromatographic and enzymatic methods. The most efficient separation of the intact and the two active site cleaved forms of the inhibitor was achieved in borate buffer at pH 10.0. T…

Water Sorption on Mesoporous Aluminosilicate MCM-41

Characterization of the interaction of water with the highly ordered mesoporous solid MCM-41 (pore diameter ∼2.5 nm) is undertaken with the aid of several techniques (adsorption gravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and controlled rate-evolved gas analysis). The relatively complex water-MCM-41 interactions are characterized by a type V isotherm indicating an initial repulsive character followed by a capillary condensation step of the adsorbate. This highlights both hydrophobic and hydrophilic properties of this potential model mesoporous adsorbent.

ChemInform Abstract: Kinetics of Formation of the Zeolite ZSM-11.

Influence of temperature on the behaviour of small linear peptides in capillary electrochromatography

The influence of temperature, T, on the retention times, peak widths, peak symmetry coefficients and theoretical plate numbers of two small linear peptides, [Met5]enkephalin and [Leu5]enkephalin, has been studied with capillary electrochromatography (CEC) capillary columns of 100 microm I.D. and 250 mm packed length with a total length of 335 mm, containing 3 microm Hypersil n-octadecyl bonded silica. With increasing column temperature from 15 to 60 degrees C, the electroosmotic flow (EOF) and the column efficiencies increased, whereas the retention coefficients (Kcec) of both peptides decreased. A linear relationship was found between the EOF value and the square root of the temperature ov…

Enrichment of proteinaceous materials on a strong cation-exchange diol silica restricted access material: protein–protein displacement and interaction effects

A study of size exclusion and enrichment of proteins employing strong cation-exchange diol silica restricted access material (SCX-RAM) under saturation conditions is presented. Experiments were carried out with bacitracin, protamine, ribonuclease, lysozyme and bovine serum albumin as individual proteinaceous analytes as well as comprehensive binary mixtures and with human urine samples. Protein size dependent capacity features of the SCX-RAM column was observed. Bacitracin demonstrated the highest capacity followed by protamine while adsorption capacities of both ribonuclease and lysozyme were found smaller by a factor of 10. Applying binary protein samples occurring displacement effects we…

PFG n.m.r. study of diffusion anisotropy in oriented ZSM-5 type zeolite crystallites

ZSM-5 zeolite crystallites are oriented by introducing them into a system of parallel capillaries. In this way, by applying pulsed-field gradient (PFG) n.m.r., a direct measurement of the orientation dependence of diffusion in ZSM-5 crystals has become possible. Using methane as a diffusant, the ratio D xy /D z between the diffusivities in the xy plane and in the z direction has been found to be of the order of 4.5. This value is in satisfactory agreement with the behavior expected from both MD calculations and a random walk model of molecular propagation in the two-channel network of ZSM-5-type zeolites.

Concepts of Miniaturized and Fast GC and HPLC Analytical Systems Integrated in Microreactors

Requirements of an analytical system for the analysis of the products of ethenoxide and propenoxide synthesis are discussed in relation to the specific features of the microreactor technology. A selection of suitable stationary phases and column techniques are considered and preliminary results on the analysis of synthetic mixtures of compounds of ethenoxide synthesis are presented.

Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption

Methods of nonlocal density functional theory (NLDFT), proposed recently for predictions of adsorption equilibrium and calculations of pore size distributions in micro- and mesoporous materials, were tested on reference MCM-41 materials. Five newly synthesized MCM-41 adsorbents with presumably uniform pore channels varying from 32 to 45 Å were characterized by X-ray diffraction (XRD), nitrogen adsorption at 77 K, and argon adsorption at 77 and 87 K. New sets of intermolecular interaction parameters of the NLDFT model for N2 and Ar adsorption on MCM-41 were determined. The parameters were specified to reproduce the bulk liquid-gas equilibrium densities and pressures, liquid-gas interfacial t…

Characteristics of Optimization in Individual HPLC Modes: Sections 2.2– 2.5

ChemInform Abstract: Photoluminescence of Chromium(III)-Doped Silicoaluminophosphate with AFI Structure.

A fast two-point method for gas adsorption measurements

Tailored syntheses of nanostructured silicas: Control of particle morphology, particle size and pore size

Ordered mesoporous silicas with spherical morphology and average particle size in the range between 100 nm and 2 μm were synthesised according to two novel routes. Both synthesis routes used tetraethoxysilane, water, alcohol and aqueous ammonia for producing spherical silica beads. The porosity was created by adding two different kinds of pore structure directing agents to the starting solution: one was an n-alkyltrialkoxysilane which was covalently bonded to the silica framework, the other was an n-alkylamine which acted as a nonionic template. After calcination and post treatment the resulting particles showed a specific surface area up to 1000 m2 g-1, a specific pore volume of up to 0.8 …

Zeolithe als Adsorbentien für die Trennung, Reinigung und Konzentrierung von organischen Wertprodukten in der präparativen Säulen-Flüssig-Chromatographie

The Basic Idea and the Drivers

Preliminary studies on the synthesis of alkaline-free large crystals of ZSM-5

Single crystals of ZSM-5 were synthesized in three systems containing Na + -TPA, Li + -TPA, and NH 4 + -TPA, respectively. Applying a reaction mixture of the molar composition 8 TPA + 123(NH 4 ) 2 O + Al 2 O 3 + 59 SiO 2 + 2280 H 2 O, alkaline-free, homogeneous, and pure single crystals of ZSM-5 were prepared up to a length of 350 μm. The crystal size and yield were found to be dependent on the water content of the starting reaction mixture and on the type of aluminium source; for example, boehmite and aluminiumtriisopropylate.

Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)

This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed…

Improvement of Raman Spectra of SAPO-5 by Chromium(III)-Induced Luminescence Quenching

Novel route in the synthesis of MCM-41 containing framework aluminum and its characterization

Abstract Mesoporous molecular sieve MCM-41 with incorporated structural aluminum (Al-MCM-41) was prepared by hydrolysis of a solution of tetraethoxysilane and aluminum isopropoxide in the presence of ammonia as a catalyst. This method provides Al-MCM-41 of different Si/Al ratios from 13 to 297 corresponding to 0.3–7 mol% Al within an hour. X-ray diffraction and nitrogen adsorption measurements showed that the Al-MCM-41 prepared by this method had a highly ordered structure of pore arrays. Most Al atoms in these samples were incorporated tetrahedrally in the MCM-41 structure, which gave rise to cationic sites in the framework.

Surfactant based synthesis of oxidic catalysts and catalyst supports

The preparation of mesostructured metal oxides based on the surfactant controlledsynthesis of MCM-41 is presented. It can be expected that the new metal oxide materials will exhibit a high surface area of nearly 1000 m 2 /g and could have a possible use as catalysts, especially in partial oxidation reactions and as hosts for quantum sized material, if the surfactant can be removed without destroying the structure.

NMR Studies of Single-File Diffusion in Unidimensional Channel Zeolites

Single-file diffusion is the restricted propagation of particles that cannot pass each other. The occurrence of this phenomenon should be reflected by a change in the time dependence of the mean particle displacement in comparison with ordinary diffusion. Although this process is considered to be the rate-controlling mechanism in a large variety of processes, so far no direct evidence of this phenomenon has been provided. Diffusion measurements made with pulsed field gradient nuclear magnetic resonance (NMR) in unidimensional pore systems (zeolites AlPO4-5 and Theta-1) reflect the expected time dependence of single-file diffusion.

Synthesis and properties of chemically modified dihydroxy-, hydroxyamino- and amino-functional silica packings in adsorption chromatography

1,2-Dihydroxy-3-propoxypropyl (HPP), 1-amino-2-hydroxy-3-propoxypropyl (AHP) and 3-(2-aminoethylamino)propyl (AEAP) silica packings were synthesized by means of both a surface modification and a bulk modification procedure. In surface modification a complete monolayer of bonded groups could be achieved. The modifiers reacted with the silanol groups according to a bifunctional mechanism. Eluotropic series of solvents were established on these polar modified silicas referring to n-heptane having ɛ∘=0. The solvent parameter ratio of modified to bare silica was found to be constant over a wide range of solvent compositions as \(\varepsilon _{{\text{HPP - silica}}}^ \circ = 0.26\varepsilon _{{\t…

Direkte Kopplung der Hochdruckextraktion mit verflüssigten und überkritischen Gasen mit der Hochdruckflüssig-Chromatographie

Study of conformational effects of recombinant interferon gamma adsorbed on a non-porous reversed-phase silica support.

Abstract Reversed-phase chromatography is a powerful method for separating recombinant interferon γ and one of its analogues differing only by a single amino acid residue. Structural differences of the proteins explain this separation ability as demonstrated from adsorption studies on a non-porous reversed-phase support. To reveal the structural differences occurring in the adsorbed state, two different and independent methods were employed. The variation of the retention with the slope of the linear gradient gave information about the molecular contact area of the protein with the support. For different experimental conditions, these data were correlated with the adsorbent capacities measu…

Impact of pore structural parameters on column performance and resolution of reversed-phase monolithic silica columns for peptides and proteins

In this work, monolithic silica columns with the C4, C8, and C18 chemistry and having various macropore diameters and two different mesopore diameters are studied to access the differences in the column efficiency under isocratic elution conditions and the resolution of selected peptide pairs under reversed-phase gradient elution conditions for the separation of peptides and proteins. The columns with the pore structural characteristics that provided the most efficient separations are then employed to optimize the conditions of a gradient separation of a model mixture of peptides and proteins based on surface chemistry, gradient time, volumetric flow rate, and acetonitrile concentration. Bo…

SilicaROD™ — A new challenge in fast high-performance liquid chromatography separations

Abstract High performance liquid chromatography (HPLC) has become one of the most used methods for the analysis of compound mixtures in industry, especially for the quality control of products. Nowadays productivity is the major and dominant upcoming issue, i.e. the goal is to drastically reduce the analysis time and cost per analysis. The solution of the task is higher throughput and faster HPLC methods. Here we describe a new monolithic type of HPLC column, the SilicaROD™ column, which permits the fast HPLC separation of compound mixtures within a few minutes.

The synthesis of zeolites from dry powders

Summary ZSM-5 was synthesized by different methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO 2 * Al 2 O 3 gels at 650°C were transformed into zeolites in the presence of dried NH 4 F and TPABr. The reaction products were characterized by XRD, REM, TG/DTA, MAS NMR and Electron Micropobe. Pure ZSM-5 or Silicalite-1 was obtained in all cases. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure at the given reaction conditions. To explain the formation of…

A novel approach to polymer-template mesoporous molecular sieves

A novel synthesis route was developed to produce spherical silica particles. The synthesis is based on a modified Stoeber method and the room-temperature synthesis of MCM 41S-materials applying tetraethoxysilane, alcohol, water, ammonia and homopolymers as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 5 – 1,000 m2/g; 0.1 – 1.0 cm3/g and 2-50 nm. With respect to catalytic applications hetero-atoms e.g. Al were incorporated into the silica framework.

Particle packed columns and monolithic columns in high-performance liquid chromatography-comparison and critical appraisal

The review highlights the fundamentals and the most prominent achievements in the field of high-performance liquid chromatography (HPLC) column development over a period of nearly 50 years. After a short introduction on the structure and function of HPLC columns, the first part treats the major steps and processes in the manufacture of a particle packed column: synthesis and control of particle morphology, sizing and size analysis, packing procedures and performance characterization. The next section is devoted to three subjects, which reflect the recent development and the main future directions of packed columns: minimum particle size of packing, totally porous vs. core/shell particles an…