Regularities of the retention of aminopyridines by silica gel modified with gold nanoparticles

New sorbents based on silica gel and gold nanoparticles stabilized by L-cysteine and its methyl ester are synthesized. Regularities of the retention of various substituted aminopyridines by the synthesized sorbents are examined in the normal-phase mode of high-performance liquid chromatography upon elution by a binary mobile phase (hexane-isopropanol). Quantum-chemical simulations of L-cysteine and its derivative adsorptions on the surface of a gold cluster are performed, along with simulations of subsequent adsorptions of substituted pyridines on the modified gold surface. It is shown that the Snyder-Soczewinski and Scott-Kucera displacement models can be used to describe the experimental data on the synthesized sorbents.     

Characterization of polyimide sorbents by using tracer pulse chromatography

A modification of tracer pulse chromatography was used to rapidly evaluate four novel polyimide sorbents for use in air sampling. This technique utilized probe molecules with differenet functional groups to evaluate the surface retention characteristics when the sorbents were highly loaded by these chemicals and humidity. The evaluation of sorbents indicated the polymer subunits of each must have multiple sorption sites which is consistent with their chemical makeup. Some comparisons between the polyimides and Tenax-GC were made.     

Affinity extraction of emerging contaminants from water based on bovine serum albumin as a binding agent

Affinity sorbents using bovine serum albumin as a binding agent were developed and tested for the extraction of environmental contaminants from water. Computer simulations based on a countercurrent distribution model were also used to study the behavior of these sorbents. Several model drugs, pesticides, and hormones of interest as emerging contaminants were considered in this work, with carbamazepine being used as a representative analyte when coupling the albumin column on‐line with liquid chromatography and tandem mass spectrometry. The albumin column was found to be capable of extracting carbamazepine from aqueous solutions that contained trace levels of this analyte. Further studies of the bovine serum albumin sorbent indicated that it had higher retention under aqueous conditions than a traditional C₁₈ support for most of the tested emerging contaminants. Potential advantages of using these protein‐based sorbents included the low cost of bovine serum albumin and its ability to bind to a relatively wide range of drugs and related compounds. It was also shown how simulations could be used to describe the elution behavior of the model compounds on the bovine serum albumin sorbents as an aid in optimizing the retention and selectivity of these supports for use with liquid chromatography or methods such as liquid chromatography with tandem mass spectrometry.     

High-Performance Chelation Chromatography of Metal Ions on Sorbents with Grafted Iminodiacetic Acid

The chromatographic behavior of some alkaline-earth, transition, heavy, and rare-earth metals on a number of complexing sorbents containing surface iminodiacetic acid (IDA) functional groups is studied. The conditions under which metal retention is determined by complexation on the sorbent surface were established, and the main principles of a new variant of the liquid chromatography, i.e., high-performance chelation ion chromatography (HPCIC), are formulated. The efficiency and selectivity of separation of the metal ions are considered depending on the type of the IDA bonding, the sorbent matrix parameters, the eluent composition, and the temeprature of the chromatographic column. Under optimal conditions, the metal retention is shown to linearly correlate with the stability constants of the respective complexes in the double-logarithmic scale. The application of HPCIC to the analysis of multicomponent systems is considered.     

Modelling of n-alkane retention and optimization of the conditions for analysis in gas adsorption chromatography with temperature programming

Summary The possibility of constructing a mathematical model of n-alkanes retention upon their separation by gas solid chromatography with temperature programming has been studied. The functional dependence between the number of the carbon atoms in n-alkane molecules, their retention in isothermal conditions and temperature of chromatographic column was used for constructing this mathematical model. It showed necessary to take into account the variance in the process temperature programming of both the carrier gas volume velocity and the column inlet pressure to obtain the adequate mathematical model of the chromatographic retention. With the use of the specific retention parameters of substances i.e. relative to the surface or the mass of sorbents the proposed model can be used not only for Silochrom C-80 but for the whole class of macroporous silica sorbents.     

Microcolumn liquid chromatography on carbon sorbents

Summary The retention volume dependences on the molar volume were found for aromatic compounds using liquid microcolumn chromatography. The contributions of the functional groups in molecules of these compounds to the total retention value were calculated from the capacity factor values. The comparison of capacity factor values for carbon sorbents and octadecyl-silicagel has shown that for several microcolumn separations the carbon sorbent column has a better selectivity and resolution than the octadecyl-silicagel column.     

Nitrate-Citrate Sol-Gel Synthesis of Hydrated Calcium Aluminate and Sorption Materials on Its Basis

Sol-gel technique was used to develop a method for synthesis of hydrated tricalcium aluminate Ca₃[Al(OH)₆]₂ and surface-layered gas-chromatographic sorbents on its basis. The materials obtained were examined by X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence microanalysis, adsorption porosimetry, and gas chromatography. It was found that cubic Ca₃[Al(OH)₆]₂ is the main phase in the surface layer of the sorption materials. The Hammett indicator method was used to examine the acid-base properties and the variation of the content of active centers between sorbents obtained in different ways. The chromatographic retention parameters were determined for test compounds, and the polarity and selectivity of the sorbents under study was evaluated. It was shown that Chromaton N-AW modified with hydrated calcium aluminate can be used, with addition of SE-30 stationary liquid phase, to separate complex mixtures of organic compounds.     

Gas-solid elution chromatography in a column with surface-layer biporous packing

The theory of gas-solid elution chromatography on surface-layer biporous packing was examined. The explicit analytical expressions for the dependences of HETP and retention time on the thickness of the surface porous layer were obtained. The use of the surface-layer packing makes it possible to increase the separation efficiency as compared to the conventional sorbents. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 340–342, February, 1999.     

A study of the adsorption properties of the hypercross-linked polystyrene sorbents Styrosorb by gas chromatography. Effect of the conditioning temperature

The effect of the conditioning temperature of the hypercross-linked polystyrene sorbents Styrosorb on the retention ofn-hexane, benzene. and acetone was studied by gas chromatography. The rigid but mobile structure of 100% cross-linked polymers with a specific surface area of 300–500 m² g⁻¹ prepared in cyclohexane slightly shrinks by conditioning above 200 °C. This results in a significant increase in the specific retention volumes of the adsorbates. The commercial hypercross-linked sorbents MN-100 and MN-200 with specific surface areas of −1000 m² g⁻¹ retain their structure up to 250 °C. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1502–1506, August. 1999.     

Sol-gel synthesis and sorption properties of calcium monoaluminate

Method for synthesis of calcium aluminate and sorbents based on this compound was developed on its basis of the sol-gel technology. The method makes it possible to obtain the target product with specific surface areas in the range from 7 to 120 m² g^–1. The compounds obtained were characterized by scanning electron microscopy, X-ray phase analysis, and X-ray fluorescence microanalysis. It was found that the main phase of the sorbents is rhombohedral calcium monoaluminate CaAl₂O₄. The method of Hammett indicator adsorption was used to determine the content of active centers on the surface of the sorbents and the distribution of these centers over ionization constants. It was shown that the surface characteristics of the sorbents depend on their synthesis method. The retention parameters, polarities, and thermodynamic characteristics were determined for organic compounds of various classes. The possibility of using calcium aluminate modified with sodium chloride for gas-chromatographic separation of aliphatic and aromatic hydrocarbons and carbonyl compounds was demonstrated.     

Nanoporous carbon sorbent for molecular-sieve chromatography of lipoprotein complex

The physicochemical characteristics of carbon sorbents are investigated. Electron microscopy data for the sorbent and separated lipoprotein complex are presented. It is found that the obtained carbon sorbent possess high porosity. Nanoporous carbon sorbents for the chromatography of molecular-sieve markers are obtained and tested. The applicability of nanoporous carbon sorbents for separation of lipoprotein complexes (LPC) is investigated.     

Adsorption of aromatic compounds from solutions in <Emphasis Type="Italic">n</Emphasis>-heptane by modified nanoporous silica

The adsorption of anisole, anthracene, benzoic acid, benzene, naphthalene, phenanthrene, phenol, and carbon tetrachloride from dilute solutions in n-heptane on the modified nanoporous silica sorbents, Silasorb C18 and Phenyl-Silasorb, at 298 K is investigated by developing liquid chromatography. The Henry law constants and Helmholtz energy of adsorption for these aromatic compounds are calculated from their retention values. The adsorption isotherms of the aromatic compounds are calculated from their chromatographic peaks with allowances made for longitudinal smearing. A correlation is made between the Henry law constants calculated from the retention values of the aromatic compounds and from their adsorption isotherms. The influences of the surface modification of the silica adsorbents and the molecular structure of the aromatic compounds on their elution from the chromatographic column with n-heptane as the eluent are discussed. Contributions of functional groups in the molecules of the aromatic compounds to the Helmholtz energy of adsorption on different surfaces are estimated.     

The use of solid sorbents for direct accumulation of organic compounds from water matrices–a review of solid-phase extraction techniques

The main principles of solid-phase extraction techniques are reviewed in this paper. Various solid sorbents can be used as a suitable trap for direct accumulation of organic compounds from aqueous solutions. The trapped analytes can be desorbed by elution with suitably chosen liquid phases. These preconcentration procedures can be considered as low performance liquid chromatography and the efficiency of the procedure can thus be related to the retention characteristics of the preconcentration column. The main sorbents used for trace enrichment purposes are also reviewed. Besides, the concise methodology, sample storage, and automation are discussed. The advantages of solid phase extraction as compared to liquid-liquid extraction are given as well as some drawbacks of this method.     

Gas-chromatographic identification of fluorine-containing organic compounds

The gas-chromatographic retention of a series of fluoroalkylarenes on the standard nonpolar polydimethylsiloxane stationary phase OV-101 was characterized, and the retention indices of these compounds were determined. It was found that large negative values of the homological increments of these constants can serve as a sign of fluorine derivatives that contain no less than three fluorine atoms per molecule. The retention indices on polar inorganic sorbents, the silica gels Silipor 75 and Silipor 600, were chosen as the second chromatographic parameter. On these sorbents (unlike partition separation), the nonadditivity effect of the retention indices of polyfunctional organic compounds with respect to their simpler structural analogs was found for the first time. It was found that a mutual correlation between indices for this combination of a phase and a sorbent was lower than that for the combinations of phases with different polarities; this fact is responsible for the higher information content of this combination for the identification of compounds from this class.     

The calculation of retention and selectivity in reversed-phase liquid chromatography II. Methanol-water eluents

Summary To calculate retention in reversed-phase, high-performance liquid chromatography a method based on the molecular structure of the analyte and the characteristics of sorbents and mobile phases has been employed. Characteristics of different ODS-columns in water-methanol eluents have been determined.     

用前沿色谱法测定蛋白质吸附等温线时增浓方式的研究

用连续前沿色谱法和断续前沿色谱法测定了七种标准蛋白在疏水色谱填料上的吸附等温线,两种方法之间存在着一定的差别。从流出曲线突跃处斜率测定的不确定性、色谱过程中动力学因素和实验方法本身存在的问题等几个方面探讨了误差的来源,指出了可能解决这一问题的途径。     

Thin-layer chromatographic and high-performance thin-layer chromatographic ready-for-use layers with lipophilic modifications

Stable silica gel sorbents with aliphatic or aromatic groups are formed by chemical modifications of the silanol groups with special reactive silanes. Various lipophilic surface modifications on silica gels with varying pore structures are tested with regard to their chemical and physico-chemical characteristics, their wettability and their chromatographic retention data. The main problem in TLC is the preparation of abrasion-resistant layers on glass or on foils which meet the usual high standard of quality and are also suited for quantitative determinations. Thin-layer chromatography on reversed-phase layers can only be performed if the complete wettability of the lipophilic stationary phase in dry form is guaranteed by the mobile phase. Adsorption-chromatographic separations with lipophilic eluents and reversed-phase partition-chromatographic separations with hydrophilic eluents are performed, for example, with dyes, with polycyclic aromatic hydrocarbons and with lipids. The great differences in selectivity caused by the various modifications of the sorbent and the varying eluent composition are remarkable. Ready-for-use layers with lipophilic surface modifications complement the existing range of pre-coated layers and thus widen the application of TLC and HPTLC considerably.     

Evaluation of metal fractions in river sediments and waters: application of chelation chromatography-differential pulse anodic stripping voltammetry

The ability of chelation chromatography in combination with differential pulse anodic stripping voltammetry (DPASV) to provide a simple, fast and reliable way of dealing with interionic interferences, competitive complexations, re-adsorption of released metal ions and sorption of spiking metal ions by organic/inorganic materials in the complex matrixes of real natural samples has been critically examined. The technique is based on the selective complexation of target metal fractions on some novel sorbents which are polymeric chelating resins doped on stationary supports (Whatman No. 1 paper and silica gel). The usual complications of leaching of the resin and/or the chelating ligand and colloid retention on the sorption bed at any stage of separation were largely obviated with these sorbents under the operational conditions of metal sorption. A detailed study on the application of such sorbents to the differentiation of ionic (free), labile (ionic plus weakly complexed) and bound (strongly complexed) metal fractions present in local river-sediment and water samples was carried out. Chelating resin-impregnated paper (CRIP) and chelating resin-immobilized silica gel column (CRISC) methods of chromatographic separation of analyte trace metals in combination with the follow-up 'standard addition' procedure of the DPASV technique were employed. A modest attempt has been made to formulate a speciation (fractionation) scheme for metal contents present in river-sediments and waters on the basis of selective retention of ionic and labile fractions on complexing resins.     

Interaction of Water and Methanol Molecules with the Surface of Carbonaceous Materials According to Gas Chromatographic Data

We have used gas chromatography to study the interaction of water and methanol molecules with active hydrophilic centers on the surface of thermally expanded graphite and graphitized thermal carbon black. We have determined the concentration of carboxyl and phenol hydroxyl groups on the surface of the sorbents and the heats of adsorption for adsorption of the studied substances on these groups. We have shown that water molecules are adsorbed as clusters on the hydrophilic centers of the studied sorbents at very low relative pressures, with n = 2 molecules in the cluster.