Dynamic Preconcentration of Organic Substances on Nonpolar Adsorbents

The possibilities of using dynamic adsorption preconcentration in the determination of organic substances were discussed. The effect of thermodynamic and kinetic factors on the extraction of organic compounds from aqueous solutions was considered. The main classes of adsorbents were presented, and the relationship between the adsorbent properties and the efficiency of preconcentration was discussed. Examples of using dynamic adsorption preconcentration for the determination of a wide spectrum of substances were given.     

Kinetic and Dynamic Aspects of Arsenic Adsorption by Fe(III)-Loaded Sponge

Nowadays there is a great concern about new adsorbent materials for either the removal or fixation of arsenic species because of their high toxicity and the health problems associated with such species. In this paper the kinetics of absorption of As(V) on Fe(III)-loaded sponge have been studied and the results are compared with those of other natural and synthetic adsorbents. Arsenate was adsorbed very rapidly by Fe(III)-loaded sponge with saturation being reached in less than ten minutes. Arsenate was also adsorbed by Fe(III)-loaded Lewatit-TP-207 and non-loaded Purolite A100S ion-exchange resins but the times required to reach total saturation of the adsorbent were more than 100 minutes. The experimental data followed first-order kinetics. The extraordinarily superior kinetics are postulated to be related to the open-celled internal structure of the sponge material. The effect of flow rate on the dynamic removal of As(V) was studied in a fixed-bed column reactor for Fe(III)-loaded sponge and Fe(III)-loaded resin. The adsorption of As(V) on fixed-bed columns of adsorbent also indicated better kinetic properties for the sponge. Column studies showed a good correlation between the experimental data and the calculated breakthrough curves obtained by the Wolborska and Clark models. Application of the Wolborska model to the data at low C/C ₀ ratios enabled the determination of the kinetic coefficient of mass transfer for the sponge and resin materials at the different flow rates used and gave a good prediction of the 5% breakthrough times. Furthermore, the breakthrough curves were well described by the Clark model at the ratios of concentration of effluent to influent up to 0.5 for the sponge and 0.3 for the Fe(III)-loaded resin. Above these levels, a large deviation occurred for the resin adsorption. Thus, the sponge was found to be kinetically effective and favored for As(V) adsorption from solution over the conventional adsorbents used and for most of the adsorbents reported in the bibliography.     

Influence of the ionic form of a cation-exchange adsorbent on chromatographic separation of galactooligosaccharides

Separation performance of sodium, lithium, potassium and hydrogen ionic forms of a commercial cation exchanger, Diaion UBK 530, based on a styrene-divinylbenzene copolymer resin support was studied. The adsorbents were applied to the separation of galactooligosaccharides from their mixture with lactose, glucose and galactose. Separation performance of the hydrogen ionic form of the adsorbent was superior to that of other adsorbent forms. A much higher yield of galactooligosaccharides of the requested purity was achieved for this adsorbent form owing to its better kinetic properties. Adsorption properties of individual adsorbents were discussed in relation to possible adsorption mechanisms.     

Speciation of ultra-trace amounts of inorganic arsenic in water and rice samples by electrothermal atomic absorption spectrometry after solid-phase extraction with modified Fe3O4 nanoparticles

A new magnetic adsorbent, 3-mercaptopropionic acid coated 3-aminopropyl triethoxysilane modified Fe₃O₄ nanoparticle, was synthesised and used for the extraction and preconcentration of arsenic ions in aqueous solutions followed by electrothermal atomic absorption spectrometric determination. The adsorbent was characterised by TEM, SEM, XRD and FT-IR techniques and the method used the unique properties of magnetic nanoparticles, namely, high surface area and superparamagnetism which gave it the advantages of high extraction capacity, fast separation and low adsorbent consumption. Different parameters affecting extraction efficiency of the analyte including pH value, sample volume, adsorbent amount, extraction time and desorption conditions were investigated and optimised. Under the optimum conditions, wide linear range of 30–25,000 ng L^?1 and low detection limit of 10 ng L^?1 were obtained. The interday and intraday precisions (as RSD%) for five replicates determination of 50 and 25,000 ng L^?1 of arsenic ions were in the range of 2.3–3.2%. Furthermore, no significant interference was observed in the presence of coexisting ions and high preconcentration factor of 198 was obtained. The adsorption isotherm followed Langmuir model and its kinetic was second-order. The accuracy of the method was validated by analysing certi?ed reference materials for water and rice with satisfactory recoveries. Finally, the proposed method was successfully applied for the determination of ultra-trace amounts of arsenic in rice and water samples.     

Extraction and Separation Properties of Hydrophilic Compounds Using Novel Water-Holding Adsorbents Bonded with a Zwitter-Ionic Polymer

A novel water-holding adsorbent was synthesized by introducing a zwitter-ionic polymer to a hydrophilic methacrylate base resin. The retention abilities of the hydrophilic compounds on the adsorbents with and without cross-link in the zwitter-ionic functional groups were examined. The amount of held water on the non-cross-linked adsorbent was higher than that of the cross-linked one. The extraction efficiencies of the hydrophilic solutes on the adsorbents were evaluated by the solid phase extraction method. These adsorbents showed high affinity for nucleosides and glycosides, and good recoveries for such hydrophilic compounds in the solid-phase extraction were obtained. Furthermore, the retention properties of the hydrophilic solutes on the adsorbents were also evaluated by LC. The hydrophilic solutes were retained on these adsorbents by a partition mode based on a hydrophilic interaction. The retention factors of the hydrophilic solutes showed good correlation to their log P _o/w (logarithm of octanol?Cwater partition coefficient) and good separation based on hydrophilic interaction was obtained for nucleobases and nucleosides.     

Preparation and modification of complex pyrolytic carbon-silica adsorbents

Summary The surface properties of complex adsorbents prepared through the pyrolysis of dichloromethane on the surface of silica gel were investigated. The reaction was carried out in a specially constructed reactor at 400–500°C. The construction and performance of the reactor are described. The modification of the silica gel surface by pyrogenic carbon results in its chemical but not energetical homogeneity. Such adsorbents usually show strong adsorptive properties which limits their use in chromatography. A simple method of homogenizing the porous structure and energetic properties of the adsorptive centers of such adsorbents is presented. The method consists of an additional pyrolysis of an alcohol or other substances on the surface of the carbon-silica adsorbent. Such reactions were carried out under both static and dynamic conditions. The properties of the modified adsorbent depend on the reaction conditions and on the type of the additionally pyrolysed substance.     

Preconcentration and quantification of copper,lead, and cadmium using anion exchangers modified with azo compounds

The sorption of azo compounds on anion exchangers of different basicity is studied; the physicochemical and analytical properties of the modified adsorbents are studied. For the prepared modified adsorbents, the conditions of the preconcentration and elution of copper, lead, and cadmium are determined. The analytical potency of the adsorbent Amberlite-Zincon for the group preconcentration and isolation of copper, lead, and cadmium from solutions of complex composition is demonstrated. An efficient combination procedure for the determination of copper, lead, and cadmium in geothermal waters are developed.     

Characterization of intercalated iron(III) nanoparticles and oxidative adsorption of arsenite on them monitored by x-ray absorption fine structure combined with fluorescence spectrometry

This paper first deals with the screening and optimization of Fe(III)-based adsorbents for arsenic adsorption from 0.2 to 16 ppm test solutions of arsenite/arsenate. The best adsorption capacity has been reported on alpha-FeO(OH) on an adsorbent weight basis. Better results were found on intercalated Fe-montmorillonites for arsenite adsorption below the equilibrium dissolved As concentration of 310 ppb and for arsenate adsorption in all of the concentrations studied. Next, the speciation of As adsorbed was performed by As K-edge x-ray absorption fine structure (XAFS) combined with high-energy-resolution fluorescence spectrometry. Major oxidative adsorption of arsenite was observed on Fe-montmorillonite from the 0.2-16 ppm test solutions. The reasons for the higher capacity of arsenic adsorption and oxidative adsorption of arsenite on Fe-montmorillonite are discussed.     

聚对羟基苯乙烯吸附树脂的合成及对咖啡因的吸附机理研究

用正庚烷／正丁醇、正庚烷／环己醇等混合溶剂为致孔剂合成了一系列具有不同比表面积的对羟基苯乙烯－二乙烯苯共聚物,并研究了这些共聚物对咖啡因的吸附性能。结果表明：凝胶型树脂吸附量小,而大孔型树脂吸附量大且比表面积对树脂的吸附量影响不明显。ＩＲ证实这类树脂吸附咖啡因时,氢键起了非常重要的作用。     

Determinants of protein retention characteristics on cation-exchange adsorbents.

There are currently a large number of commercially available strong and weak cation-exchange adsorbents for preparative protein purification, typically prepared by coupling charged ligands to a mechanically rigid porous bead. Because of the diverse chemical nature of the base matrix (carbohydrate, synthetic polymer, inorganic) and the coupling and ligand chemistry, cation-exchange adsorbents from different suppliers can differ substantially in chemical surface properties and physical structure. The differences in chemical properties can be in ionic capacity, hydrophobicity, the presence of hydrogen bond donors/acceptors, and the nature of the charged functional groups. In order to probe the effects of these factors on protein affinity, the isocratic retention of a set of model proteins was examined on a set of cation-exchange adsorbents to obtain a quantitative assessment of retention differences between adsorbents. Two adsorbent factors were found to be the dominant determinants of overall protein retention: the anion type and the adsorbent pore size distribution. Protein retention on strong cation-exchangers was found to be greater than that on corresponding weak cation-exchangers. Protein retention was increased on adsorbents with pore size distributions that include significant amounts of pore space with dimensions similar to those of the protein solute.     

SYNTHESIS OF SPHERICAL MACROPOROUS ADSORBENT BASED ON UREA-FORMALDEHYDE CONDENSED POLYMER

INTRODUCTIONPowder-like adsorbents based on urea-formaldehyde condensed polymers were patented tobe used in the treatment of heavy metal polluted water and the removal of tannins from fruitsjuice. It is limited of this kind of adsorbent in flow-through applications due to the poor dynamicproperties. The synthesis of spherical porous adsorbent based on urea-formaldehydepolycondensate was originated from the preparation of HPLC packing materials with bead sizefrom 5 micron to tO micron by …     

SYNTHESIS OF SPHERICAL MACROPOROUS ADSORBENT BASED ON UREA—FORMALDEHYDE CONDENSED POLYMER

Spherical macroporous adsorbents with active sites capable of hydrogen bonding adsorption based on urea-formaldehyde condensed polymer were synthesized via reversed suspension polymerization.The properties of the obtained adsorbent were also investigated in detail.The results showed that the water permeability could be improved by adding hydroxyl-contatining organic compound moiety into the adsorbent.The specific surface area and average pore diameter of these adsorbents increaswed while the porosity first increased then decreased with the increase of the amount of the added hydroxyl-containing compound.     

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.     

具有高比表面积的极性吸附树脂的合成和性能研究

本文从树脂物理结构和化学结构着手，通过改变交联度，致孔剂用量，种类以及引入适量功能基因，分别合成了一系列具有高比表面积和极性的大孔吸附树脂，研究了它们对工业废水中β－萘碘酸的吸附－脱附性能．     

Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation

The paper presents results of a study on obtaining activated carbon from common corn cobs and on its use as adsorbent for removal of pollution from liquid and gas phases. The crushed precursor was subjected to pyrolysis at 500 and 800?°C in argon atmosphere and next to physical or chemical activation by CO₂ and KOH respectively. The effect of pyrolysis conditions and activation method on the physicochemical properties of the materials obtained was tested. The sorption properties of the carbonaceous adsorbents obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide sorption from gas stream in dry and wet conditions as well as by iodine and methylene blue removal from aqueous solution. The final products were microporous activated carbons of well-developed surface area varying from 337 to 1213 m²/g and showing diverse acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for corn cobs permits production of cheap adsorbents with high sorption capacity toward toxic gases of acidic character as well as different pollutants from liquid phase.     

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.     

Application of thermal desorption to the development of a gas chromatographic/mass spectrometric method for the determination of toluene,chlorinated aromatic hydrocarbons,and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combustion emissions

A fast and accurate analytical method, which uses commercially available adsorbents (Tenax TA, Carbotrap B and C, and Carbosieve S-III), was developed for the sampling and determination of aromatic hydrocarbons, chloroaromatic compounds, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The breakthrough volume data show that Carbotrap C has a good capacity for compounds of high molecular weight, whereas Carbosieve S-III and Tenax TA are efficient for volatile compounds. The organic components are thermally desorbed and transferred to a gas chromatograph/mass spectrometer. Importantly, thermal desorption avoids conventional solvent extraction procedures and also allows reuse of adsorbent tubes. Preliminary results for recovery of analytes from tubes packed with single adsorbent prove that a single-adsorbent bed is not capable of sampling a wide range of compounds. The best method to obtain the desired collection and desorption properties is to use adsorbent tubes containing several different materials. The results of optimization studies are summarized.     

Use of synthetic adsorbents in preparative normal-phase liquid chromatography

Normal-phase liquid chromatographic separation using polymeric synthetic adsorbents was investigated. The retention behavior of dialkyl phthalates under a hexane-isopropanol eluent system revealed that both polystyrenic and polymethacrylic adsorbents can be used for normal-phase liquid chromatography, and that the polymethacrylic adsorbent has stronger retentivity than the polystyrenic adsorbent. Applicability of these synthetic adsorbents, especially the polymethacrylic adsorbents, was verified by the separation of polyunsaturated fatty acids, schizandrin in Schisandra chinensis fruit, tocopherols and tocotrienols in vegetable oils using a 10-microm adsorbent packed into an HPLC column. Furthermore, the separation was expanded to preparative scale by using polymethacrylic adsorbents with 17- and 31-microm fine grade particle sizes. The effect of loading volume on the retention or separation was also examined, and separation was maintained up to the loading of several grams per liter adsorbent. These results demonstrate that commercially available synthetic adsorbents possess considerable performance as normal-phase chromatographic media for more precise purification of bioactive compounds. including pharmaceuticals and nutraceuticals with scale-up possibilities.     

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.