Method for estimating the residual silanol activity of reversed-phase chromatographic adsorbents

The retention of some organic bases on reversed-phase adsorbents was studied as a function of the concentration of KH₂PO₄ in the mobile phase. It was shown that, for some adsorbents, retention decreases with an increase in the salt concentration, while an opposite dependence was observed for the other adsorbents. Such behavior of adsorbates can be explained by the prevailing silanophilic interactions in the former case and hydrophobic interactions in the latter case. The observed dependence can be used to change the chromatographic selectivity in the analysis of complex mixtures containing organic bases and to assess the properties of reversed-phase columns. Diphenhydramine hydrochloride was proposed as a test substance to assess the properties of the columns in the analysis of multicomponent pharmaceutical preparations. It was used in the comparative study of the properties of some adsorbents.     

石墨烯基吸附剂的设计及其对水中抗生素的去除

抗生素的大量使用,所带来的环境污染问题受到广泛关注。吸附法因去除效率高、普遍适用性强,呈现出广阔的应用前景,开发新型吸附剂是高效能吸附处理的关键。近年来石墨烯优良的物理和化学性质以及吸附性能,使其成为重要的抗生素吸附剂。由于石墨烯自身的局限性以及对石墨烯吸附剂处理效能和稳定性的要求,基于石墨烯设计开发了多种石墨烯基吸附材料。而目前基于水体中抗生素的石墨烯基复合材料的设计、合成及其吸附作用机制缺乏相关的系统性综述。本文综述了目前水体中抗生素的危害,针对石墨烯基复合吸附材料中,广泛关注的磁性石墨烯吸附剂、聚合物/石墨烯吸附剂、三维石墨烯凝胶和石墨烯/生物炭吸附剂的设计和制备方法进行了总结和概述,并阐述了石墨烯基吸附材料对水体中抗生素的主要吸附作用机制。最后,本文对石墨烯基吸附材料去除水体中抗生素未来的发展方向进行了展望。     

Effects of pore structure and molecular size on diffusion in chromatographic adsorbents

Two computational approaches, namely Brownian dynamics and network modeling, are presented for predicting effective diffusion coefficients of probes of different sizes in three chromatographic adsorbents, the structural properties of which were determined previously using electron tomography. Three-dimensional reconstructions of the adsorbents provide detailed, explicit characteristics of the pore network, so that no assumptions have to be made regarding pore properties such as connectivity, pore radius and pore length. The diffusivity predictions obtained from the two modeling approaches were compared to experimental diffusivities measured for dextran and protein probes. Both computational methods captured the same qualitative results, while their predictive capabilities varied among adsorbents.     

“Salt in a porous matrix” adsorbents: Design of the phase composition and sorption properties

This review formulates the concept of target-oriented synthesis of two-component “salt in a porous matrix” (SPM) adsorbents designed for processes such as gas dewatering, moisture control, heat conversion in adsorption heat pumps, and equilibrium shifting in catalytic reactions. In terms of this approach, the requirements imposed on an ideal adsorbent, which is optimal for a particular application, are initially formulated; then, a material with nearly optimal properties is synthesized. Methods for the target-oriented synthesis of SPM adsorbents with the required properties are considered. The effects of the nature of the salt and the matrix, the salt content, the pore size of the matrix, and the synthesis conditions on the phase composition and adsorption properties of the SPM adsorbents are studied.     

Solid‐phase extraction of explosive nitramines on macroreticular polymers modified by freezing with water or acetone

A novel approach is proposed to modify the porous structure and surface properties of the polymers used in solid‐phase extraction. The approach involves soaking in water or acetone, followed by freezing in liquid nitrogen (77.4 K) and was employed for two polymeric materials: Amberlite XAD‐7 and Amberlite XAD‐16. Variations in the surface properties of the adsorbents were justified by the action of acetone and water as solvents affecting the textural and other characteristic of the materials. The initial and treated adsorbents were used in extraction of explosive nitramines from aqueous samples. The performed modifications of the polymer texture allow us to increase the recovery rate as compared with the initial adsorbents. The results were justified by the swelling of fragments of the polymers and by the additional process of sorption of nitramines. The results indicate that polymeric adsorbents can be easily modified by the soaking/freezing process and the materials can be achieved that prove usefulness for the effective separation of explosive nitramines from aqueous samples.     

Determination of residual boron in thermally treated controlled-porosity glasses, by colorimetry, spectrography and isotachophoresis

Controlled-porosity glasses (CPGs) are often applied as sorbents in chromatography. Besides having high thermal, chemical and mechanical resistance they are characterized by a very narrow pore-size distribution and the choice of mean pore diameter and porosity covers a wide range. In spite of these advantages, their range of use in chromatography is restricted because of their strong adsorption properties, which are connected with the presence of residual boron atoms in the porous CPG skeleton. The boron concentration on the CPG surface can be increased by proper thermal treatment. When CPGs are heated in the range 400-800 degrees the residual boron atoms in the network diffuse from the bulk to the surface. The paper discusses the boron content in porous glasses of different mean pore diameters and the determination of the enrichment of boron on the GPG surface, by three independent methods: colorimetry, spectrography and isotachophoresis.     

Hydrophobic interaction chromatography of proteins. I. The effects of protein and adsorbent properties on retention and recovery

The contributions of protein and adsorbent properties to retention and recovery were examined for hydrophobic interaction chromatography (HIC) using eight commercially available phenyl media and five model proteins (ribonuclease A, lysozyme, alpha-lactalbumin, ovalbumin and BSA). The physical properties of the adsorbents were determined by inverse size exclusion chromatography (ISEC). The adsorbents examined differ from each other in terms of base matrix, ligand density, porosity, mean pore radius, pore size distribution (PSD) and phase ratio, allowing systematic studies to understand how these properties affect protein retention and recovery in HIC media. The proteins differ in such properties as adiabatic compressibility and molecular mass. The retention factors of the proteins in the media were determined by isocratic elution. The results show a very clear trend in that proteins with high adiabatic compressibility (higher flexibility) were more strongly retained. For proteins with similar adiabatic compressibilities, those with higher molecular mass showed stronger retention in Sepharose media, but this trend was not observed in adsorbents with polymethacrylate and polystyrene divinylbenzene base matrices. This observation could be related to protein recovery, which was sensitive to protein flexibility, molecular size, and conformation as well as the ligand densities and base matrices of the adsorbents. Low protein recovery during isocratic elution could affect the interpretation of protein selectivity results in HIC media. The retention data were fitted to a previously published retention model based on the preferential interaction theory, in terms of which retention is driven by release of water molecules and ions upon protein-adsorbent interaction. The calculated number of water molecules released was found to be statistically independent of protein retention strength and adsorbent and protein properties.     

Matrix effect on the enantiorecognition ability of adsorbents based on heptakis(6-amino-6-deoxy)-β-cyclodextrin

Four adsorbents were synthesized by immobilizing a chiral selector, heptakis(6-amino-6-deoxy)-β-cyclodextrin, on different silica matrices, such as LiChrosorb Si 100, 10 μm; Silasorb SPH Amin, 5 μm; Kromasil 100-5-Sil, 5 μm; and Kromasil 300-5-Sil, 5 μm. The surface of adsorbents was examined by low-temperature nitrogen adsorption, and the structural properties of substrates and adsorbents were studied by electron microscopy. A matrix effect on the enantiorecognition ability of adsorbents was studied in the reversed-phase and polar-organic modes of high performance liquid chromatography using some amino acid derivatives (N-carbobenzyloxy-and tert-butoxycarbonyl-) and profens as examples. The adsorbent based on Kromasil 100-5-Sil possesses the best chromatographic properties. It was shown that the enantiomeric composition and the concentration of the active component in Ibuprofen can be determined.     

Characterization of synthetic adsorbents with fine particle sizes for preparative-scale chromatographic separation

Synthetic adsorbents with fine particle sizes (15-30 microm) were manufactured. These adsorbents are made of poly(styrenedivinylbenzene) and polymethacrylate, and have the same chemical structure as analytical- (5-10 microm) or industrial- (200-600 microm) grade synthetic adsorbents. Both of them have very similar porous structure to those of analytical or industrial sizes, so that they can adsorb compounds of various molecular masses. Chromatographic separation characteristics of newly manufactured fine-particle grades of synthetic adsorbents were evaluated and compared to those of analytical or industrial adsorbents. Reasonable dependency of separation performance on particle size of synthetic adsorbents was obtained. Hydraulic properties of fine-grade adsorbents had also been measured in view of column operations. Furthermore, scalability and applicability of these adsorbents for preparative-scale chromatographic separation of bioactive compounds was evaluated. Separation of soybean isoflavones and tea catechin derivatives had revealed that fine-grade synthetic adsorbents could be well applied with scalability under the same elution conditions used for analytical use. Scalability up to a 22400-fold loading amount was achieved from a small column packed with analytical-grade adsorbent used for method development to a scale-up preparative column packed with fine-grade adsorbent used for preparative purification. These results showed the usefulness of the fine-grade synthetic adsorbents for more precise purification of bioactive compounds, including pharmaceuticals and functional food additives with higher recovery.     

Properties of new fibrous adsorbents with amidoxyme and hydrazidine groups

Data on sorption properties of new fibrous adsorbents with respect to heavy metals are presented. The POLYORGS 34 and POLYORGS 35 filled fibrous adsorbents and POLYORGS 33 fibrous adsorbent contain amidoxyme and hydrazidine groups. Is has been shown that these adsorbents can be used for the adsorption preconcentration of heavy, noble, and rare metals and radionuclides from aqueous salt solutions. Examples of using adsorbents under study for the dynamic preconcentration of copper from a 0.5 M NaCl solution during filtration through a series of disks, column, or adsorption cartridges are presented.     

Adsorption of graphene for the removal of inorganic pollutants in water purification: a review

Graphene has aroused widespread attention as a new type of adsorbents due to its outstanding ability for the removal of various pollutants from aqueous solutions. This review summarizes the application of graphene-based nanomaterials as an advanced adsorbent for the removal of inorganic pollutants including anionic and cationic type. The adsorption properties, mechanisms, isotherms, kinetics, thermodynamics and regeneration of adsorbents are all summarized, and the further research trends on graphene-based nanomaterials in the removal of pollutants are also given.     

Gas Chromatography on Zeolite-Based Adsorbents

The adsorption and gas chromatographic properties of zeolites, both modified with carbon and supported as a surface-porous layer, have been studied. Carbonization of zeolites changes the chemical nature of their surface and their molecular sieve properties. In comparison with other adsorbents (carbons, polymers, etc.), modified and supported zeolites are characterized by better selectivity for separation of light-boiling compounds formed in many catalytic reactions. Zeolite-based adsorbents have been used for gas chromatographic analysis of mixtures the analysis of which was a problem or was impossible with traditional chromatographic columns.     

Adsorption and catalytic properties of peroxidase

The adsorption of peroxidase was studied on ten silicate adsorbents, aluminosilicate, and alumina. It was shown that its value depended on both the parameters of the porous structure and the nature of the adsorbent. The maximum adsorption values were obtained on biporous silicate adsorbents and biporous aluminosilicate. It was established that the adsorbed peroxidase layers on these adsorbents had the best catalytic properties as well. It was shown that the specific activity of the enzyme depended on the degree of the surface filling.     

Development of Composite Adsorbents of Carbon and Intercalated Clay for N2and O2Adsorption: A Preliminary Study

Composite adsorbents of carbon and alumina intercalated montmorillonite were prepared and characterized by adsorption of N₂and O₂at various temperatures. The effects of pyrolysis, temperature, heating rate, subsequent degassing, and doping of cations and anions were investigated. The adsorption capacities of the composite adsorbents developed at higher temperatures (0 and −79°C) are found to be larger than those of normal alumina pillared clays. The experimental results showed that the framework of these adsorbents is made of alumina particles and clay sheets while the pyrolyzed carbon distributes in the space of interlayers and interpillars. The pores between the carbon particles, clay sheets, and alumina pillars are very narrow with very strong adsorption forces, leading to enhanced adsorption capacities at 0 and −79°C. The composite adsorbents exhibit features similar to those of carbonaceous adsorbents. Their pore structures, adsorption capacities, and selectivities to oxygen can be tailored by a controlled degassing procedure. Meanwhile, ions can be doped into the adsorbents to modify their adsorption properties, as usually observed for oxide adsorbents like zeolite and pillared clays. Such flexibility in pore structure tailoring is a potential advantage of the composite adsorbents developed for their adsorption and separation applications.     

Relative retention of the fibroblast growth factors FGF-1 and FGF-2 on strong cation-exchange sorbents

The isocratic retention of two heparin-binding fibroblast growth factors, FGF-1 (acidic FGF) and FGF-2 (basic FGF), was compared on a set of six preparative strong cation-exchange adsorbents. The FGFs comprise a solute pair that are structurally equivalent, yet differ in protein parameters of potential importance in cation-exchange chromatography, such as isoelectric point, net charge, and the number and distribution of basic amino acids. The cation-exchange adsorbents comprise a diverse set of materials in common use for protein purification, with physical and chemical properties that have been characterized and described previously. Isocratic k' values for the two proteins obtained on each adsorbent at several different [NaCl] are compared with one another and with corresponding data for hen egg lysozyme, which is also strongly retained on cation-exchangers. Of the six adsorbents examined, three showed strong retention of both FGFs, with equivalent k' values for FGF-1 and FGF-2. Three others, which showed weaker overall retention for the FGF pair, showed much larger retention differences between FGF-1 and FGF-2. The trends in retention order among the stationary phases are very similar to those seen previously with other unrelated proteins. However, retention differences between the two FGFs, and between the FGFs and lysozyme, do not correlate well with simple charge properties such as net charge, indicating, as in some previous studies, the importance of local regions on the protein surface in determining retention. These observations are interpreted in terms of the structural features of the proteins and the physicochemical properties of the adsorbents.     

Adsorbents from Waste materials

The possibility of using pyrolyzed wastes produced in already working incineration plants, as adsorbents for waste water treatment, was studied. Showing very poor adsorption properties, they were improved by steam activation technique used in the conventional activated carbon manufacturing. It is concluded that various organic waste materials can be converted to carbonaceous final products with a character similar to activated carbon. Their adsorption properties and pore size distribution are determined by the structure of the starting material. Although most of these samples have a low specific surface area, their pore volume is not negligible in the meso-and micropore range. Adsorption tests with model waste waters confirmed that adsorption properties are strongly influenced by the character of the suface. The adsorption capacity of these samples can be utilized for the treatment of strongly polluted industrial waste waters. Considering that the raw material ‘needed’ to manufacture these adsorbent is produced permanently and the adsorbents do not have to be regenerated, it might be worthwhile using these kinds of adsorbents in the primary treatment of industrial waste waters.     

Pressure-Swing Adsorption Using Layered Adsorbent Beds with Different Adsorption Properties: I—Results of Process Simulation

A simulation study was conducted on layered-bed pressure-swing adsorption, PSA, processes with adsorbents that differ in their adsorption properties. As an example, an oxygen, O₂, vacuum-swing adsorption, VSA, process was analyzed to investigate relationships between process performance and adsorption properties of the adsorbents used. For two adsorbents with identical nitrogen-to-oxygen, N₂/O₂, selectivity but different N₂ and O₂ capacities, placing the high-capacity adsorbent at the product end and the low-capacity adsorbent at the feed end of the adsorption bed gives a better performance than the case of reversing layering of these adsorbents. However, for two adsorbents with different values of N₂/O₂ selectivity but identical N₂ capacity, changing the bed-layer configuration does not show a significant difference in O₂-VSA performance. The advantages of layering a high-capacity adsorbent on product end of the bed are demonstrated by an examination of the N₂-loading difference in a VSA cycle. The modeling study also reveals an effect of cycle features (e.g., equalization step) on the effectiveness of using layered-bed configurations in VSA/PSA processes. It suggests that layering appropriately two adsorbents with different adsorption properties could result in better VSA/PSA-process performance than using a single-layer bed with either of the two adsorbents.     

Controlled release of volatile (?)-menthol in nanoporous silica materials

In this work, a series of nanoporous silica materials have been prepared as adsorbents for volatile (?)-menthol, a molecule widely used in food, pharmacy, and cosmetics. The isothermal release properties of (?)-menthol have been investigated and correlated with the structural parameters of nanoporous absorbents. A rotary evaporation method is used to effectively load (?)-menthol into the nanopores of adsorbents and to prevent the whisker growth during the adsorption. It is demonstrated that the pore size, structure, wall thickness and surface functionality of nanoporous adsorbents are four important parameters to influence the isothermal release of (?)-menthol. By tuning these parameters of nanoporous silica adsorbents, controlled release of (?)-menthol can be achieved. A vesicular silica material with thick wall and hydrophobic functional groups is shown to possess the slowest release performance. Our contribution provides important knowledge for the future applications of nanoporous silica materials in pharmacy and cosmetics.     

极性修饰的聚苯乙烯吸附树脂的结构和性能

在苯乙烯－二乙烯苯共聚体系中加入甲基丙烯酸甲酯，甲基丙烯酸，丙烯腈和乙酸烯丙酯等等三单体，对吸附树脂表面进行修饰，用物理技术和化学方法表征了合成树脂的结构，测定了它们对甜菊甙的吸附量。结果表明，第三单体的极性和用量等因素对树脂的孔结构和吸附量有较大的影响。