Material Balance Study of Adsorption of Organic Compounds

It was shown that the structure of a surface complex and the nature of an adsorption bond can be determined from the material balance of adsorption of H⁺and OH^–ions and organic compound. A calculation procedure was considered using adsorption of benzoic acid on silica gel and zirconia as examples. It was established that adsorption of benzoic acid on silica gel was accompanied by the release of H⁺ions resulted from the formation of surface hydrogen bonds, whereas adsorption on zirconia, by the substitution of OH^–ions in coordination sphere of Zr(IV).     

Hydrogenation of arenes by the RhCl3-aliquat® 336 catalyst: Part 3. Selective reduction of polycyclic compounds

Acenaphthylene, fluorene, anthracene, phenanthrene, benz[a]anthracene, pyrene, fluoranthene, benzo[c] phenanthrene and some of their derivatives were shown to undergo partial hydrogenation in the presence of the RhCl₃-Aliquat^® 336 catalyst in a highly selective manner. Olefinic double bonds were found to be hydrogenated prior to aromatic moieties. In linear aromatic molecules, only the terminal rings are reduced. In phenanthrene the C₉-C₁₀ bond and in pyrene the C₄-C₅ linkage are the only ones to be affected. Benz [a] anthracene is converted exclusively into 7,8,9,10-tetrahydrobenz[a]anthracene. Benzo[c] phenanthrene is hydrogenated to give primarily the 5,6-dihydro derivative. Chlorine and bromine substituents were found to undergo hydrogenolysis when attached to the reacting moieties, but usually remain unaffected when located on non-reacting aromatic rings.     

Retention characteristics of alkylated polycyclic aromatic hydrocarbons in normal phase liquid chromatography

Summary Retention characteristics of series of polymethyl and mono-n-alkyl derivatives of benzene and pyrene, and also of parent polycyclic aromatic hydrocarbons (PAH), were studied using silica and aminopropyl- and cyanopropyl-modified silica. Differences in the selectivities for the studied compound groups were found between the three phases. Deviations from linear behaviour in plots of log (k′)vs. carbon number were observed for the methyl series. These are explained in terms of differences in π-electron delocalisation within the aromatic ring systems. Further, the effect of methyl substitution on selectivity decreased with an increasing number of aromatic rings. Results were obtained which indicated that the primary adsorption site in a cyano column used in normal phase mode, at least for PAH molecules, is the cyano group.     

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.     

Evidence of Organic Luminescent Centers in Sol–Gel‐Synthesized Yttrium Aluminum Borate Matrix Leading to Bright Visible Emission

Yttrium aluminum borate (YAB) powders prepared by sol–gel process have been investigated to understand their photoluminescence (PL) mechanism. The amorphous YAB powders exhibit bright visible PL from blue emission for powders calcined at 450 °C to broad white PL for higher calcination temperature. Thanks to ¹³C labelling, NMR and EPR studies show that propionic acid initially used to solubilize the yttrium nitrate is decomposed into aromatic molecules confined within the inorganic matrix. DTA‐TG‐MS analyses show around 2 wt % of carbogenic species. The PL broadening corresponds to the apparition of a new band at 550 nm, associated with the formation of aromatic species. Furthermore, pulsed ENDOR spectroscopy combined with DFT calculations enables us to ascribe EPR spectra to free radicals derived from small (2 to 3 rings) polycyclic aromatic hydrocarbons (PAH). PAH molecules are thus at the origin of the PL as corroborated by slow afterglow decay and thermoluminescence experiments.     

Development and certification of a coal fly ash certified reference material for selected polycyclic aromatic hydrocarbons

The development and certification of a coal fly ash certified reference material (CRM) for polycyclic aromatic hydrocarbons (PAH) is described; this is the first natural matrix CRM for organic environmental analysis in China. The homogeneity and stability of this material have been tested by HPLC. The concentrations of several PAH were determined by use of two independent, different methods – solvent extraction–HPLC analysis with UV detection coupled with fluorescence detection (FLD) and solvent extraction, isolation with a silica column, and GC analysis with flame ionization detection (FID). Five certified values were determined: phenanthrene 7.1 ± 2.6 μg g^–1, anthracene 2.0 ± 0.8 μg g^–1, fluoranthene 7.4 ± 1.9 μg g^–1, pyrene 7 ± 2 μg g^–1, and benzo[a]pyrene 1.3 ± 0.3 μg g^–1. Reference values for several other PAH are also suggested.     

Sorbents for liquid chromatography based on the footprint principle

Summary The possibility of synthesizing normal-phase chromatographic sorbents with selectivity and specificity for an organic compound was investigated using two approaches. The generation of footprints, imprinted adsorption sites reflecting the shape of an added template molecule, was attempted by imprinting aluminum ion-doped silica gel and by modifying silica gel with diazomethane. In both cases phenanthrene was used as template molecule. Surprisingly, the diazomethane-modified silica gels showed a stronger retention for all polycyclic aromatic compounds than unmodified silica up to a carbon load of ca. 1.5%. The different gels synthesized according to the first principle showed somewhat different selectivity towards various polycyclic aromatic compounds. In neither case was a specificity toward phenanthrene observable.     

Regularities in the retention of isomeric aromatic hydrocarbons in liquid chromatography. Part I. Analysis of polymethyl-and monoalkyl benzenes and polynuclear aromatic hydrocarbons on hydroxylated silica gel

Summary The retention on hydroxylated silica gel surface upon elution with n-hexane increases in the series of polymethylbenzenes and decreases in the series of mono-alkylbenzenes (after toluene) All iosmers of xylenes, trimethyl- and tetramethylbenzenes are separated as well as isomers of tert.-phenyls, isomers of several dimethylnaphthalenes, anthracene, phenanthrene and poly aromatic hydrocarbons with five condensed rings. These separations are based on the influence of the corresponding molecule structures on the intermolecular interaction with both the adsorbent (strengthening or weakening the energy of hydrogen bonds) and the eluent (intermolecular interaction with n-hexane increases upon lengthening the alkyl group). The effect of orientation at the surface of the investigated hydrocarbon molecules on their retention is also discussed.     

Normal Phase TLC Separation of Enantiomers Using Chiral Ion Interaction Agents

Abstract

A method for the thin layer chromatographic (TLC) separation of enantiomers and diastereomers involving the use of chiral ion interaction agents is described. Several aromatic amino alcohols were resolved by TLC on diol and/or high performance silica gel plates using a mobile phase containing (1R)-(-)- ammonium-10-camphorsulfonate or N-benzoxycarbonyl-glycyl-L-proline (ZGP). Many of these chiral aromatic amino alcohols are of pharmacological importance as α- and β-adrenergic blockers, adrenergic compounds, and anti-glaucoma agents. A comparison was made between various N-CBZ-amino acid derivatives as chiral counter ions/chiral mobile phase additives (CMAs). These separations could not be achieved on other normal phase TLC stationary phases including microcrystalline cellulose, alumina and ordinary silica gel plates.     

Modification of aminopropyl silica gel with some chelating agents and their effect on its stability against hydrolysis

The stability of aminopropyl-silica gel (AP-SG) against hydrolysis was investigated after modification by 2,3-butanedione monoxime (BDMO), 8-hydroxyquinoline-2-carboxaldehyde (HQC) or isatin (Is) by Schiff’s base condensation reaction. The hybrid modified silica gel (HMSG) compounds; BDMO-SG, HQC-SG and Is-SG were characterized by IR, thermogravimetric and elemental analyses, magic angle spinning-¹³C-nuclear magnetic resonance, pH-metric titration and inductively coupled plasma–optical emission spectrometry-monitored silica hydrolysis. The stability of the HMSG’s was found to be dependant on the type of the functionalization group, which may protect the silica surface via; (1) the delocalization of the free lone pair of electrons on nitrogen of the propylamine group in the aromatic rings, which reduces local basicity experienced on the silica surface, (2) the hydrophobic nature of the organic substrates, which hinders the attack of hydroxide ions and water molecules, and (3) the bulky organic substrate, which hinders nucleophilic attack on silicon. HQC-SG is recommended as an optimal modification to meet the requirements of stability, capacity and separation efficiency of Hg(II) at pH 4.1.     

Hypercrosslinking Polymers Fabricated from Divinyl Benzene via Friedel-Crafts Addition Polymerization

Microporous organic polymers with high surface area are widely used in many applications.Among them,hypercrosslinked polymers have been extensively concerned because of their simple processes and low-cost reagents.However,due to most state-of-the-art strategies for HCPs based on condensation reactions,the release of small molecules such as hydrochloric acid and methanol involved in such strategies brings about new hazards to environment.Herein,we propose a method of fabrication of hypercrosslinked polymers via self-addition polymerization of divinyl benzene and its crosslinking with polar aromatic molecules.The hypercrosslinked polyDVB-based products are demonstrated by FriedelCrafts addition reaction of double bonds on DVB that can connect adjacent phenyl rings of aromatic molecules to form the crosslinked networks.The HCPDVB-CB obtained in 1-chlorobutane as solvent has a high micropore content and displays high surface area up to 931 m²/g.Following this finding,DVB is used as a novel external crosslinker for knitting polar aromatic molecules.When L-phenylalanine and bisphenol A are used as the aromatic units,the obtained HCP(Phe-DVB)and HCP(BPA-DVB)could reach surface area of 612 and 471 m²/g,and have hydrogen uptake of0.62 wt%and 0.58 wt%at 77 K and 1.13 bar by comparison with HCPDVB-CB having hydrogen uptake of 0.30 wt%,respectively.     

Isolation and Characterization of Sulfur-Containing Polycyclic Aromatic Compounds (Thia-Arenes) from Complex Environmental Mixtures

Abstract

A multi-dimensional chromatographic method was developed and applied to the separation of thia-arenes and polycyclic aromatic hydrocarbons (PAH) derived from coal tar. A thia-arene-rich fraction, prepared using a combination of alumina chromatography and palladium chloride/silica gel chromatography, was further separated using normal phase HPLC to isolate fractions containing thia-arenes with molecular masses ranging from 184 amu to 284 amu. These fractions were analysed using gas chromatography-mass spectrometry; approximately one-half of the thia-arenes in a coal tar extract were retained and separated by the palladium chloride-silica gel step. This methodology has been successfully applied to coal tar, air particulate material, sediments and biological samples.     

Native Mannose‐Dominant Extraction by Pyridine–Phenol Alternating Oligomers Having an Extremely Efficient Repeating Motif of Hydrogen‐Bonding Acceptors and Donors

Pyridine–phenol alternating oligomers in which pyridine and phenol moieties are alternatingly linked through acetylene bonds at the 2,6‐positions of the aromatic rings were designed and synthesized. The pyridine nitrogen atom and the neighboring phenolic hydroxyl group were oriented so that they do not form an intramolecular hydrogen bond but cooperatively act as hydrogen‐bonding acceptor and donor in a push–pull fashion for the hydroxyl group of saccharides. The longer oligomer strongly bound to lipophilic glycosides in 1,2‐dichloroethane, and association constants approached 10⁸ M ^?1. Moreover, the oligomer extracted native saccharides from a solid phase to apolar organic solvents up to the extent of an equal amount of the oligomer and showed mannose‐dominant extraction among naturally abundant hexoses. The oligomer bound to native saccharides even in 20 % DMSO‐containing 1,2‐dichloroethane and exhibited association constants of greater than 10 M ^?1 for D ‐mannose and D ‐glucose.     

Determination of Selected Persistent Organochlorine Pollutants in Human Serum by Solid-phase Disk Extraction and Dual-Column Capillary Gas Chromatography with Electron Capture Detection

Abstract

An improved clean-up method by solid-phase disk extraction was developed to isolate and concentrate trace levels of POPs (persistent organochlorine pollutants) in human serum prior to gas chromatography with electron capture detection on two different capillary columns, providing an improved selectivity. An Empore^TM C₁₈ bonded silica extraction disk cartridge is used for the initial extraction and enrichment of the analytes. Subsequent clean-up is achieved by concentrated sulphuric acid and silica gel adsorption chromatography. Recoveries for selected POPs are ranging from 62 to 74% and a good reproducibility (RSD < 14%) is demonstrated. Human samples analysed under these conditions, show a similar relative concentration profile.     

Profile analysis of polycyclic aromatic hydrocarbons by glass capillary gas chromatography in atmospheric suspended particulate matter in the nanogram range collecting 10 m3 of air

Summary A procedure is described for the analysis of polycyclic aromatic hydrocarbons containing more than 3 rings in airborne particulate matter by glass capillary gas chromatography, using a very thermostable poly-dimethyl-siloxane (CP sil 5), which does not drift in a temperature program even at the highest attenuation of the FID.In order to avoid secondary contaminations from the laboratory environment, special measures are needed. For reducing the exposition time for already collected PAH, the collecting time has been limited to 1 h (10 m³/h). The chemical destruction and re-evaporation of already collected PAH were controlled by the invariability of the PAH-profiles during the collection time (0.5 to 3 h).The influence of various solvents on the adsorption/ desorption equilibrium has been investigated. The PAH, extracted with toluene, are enriched by filtration on silica gel, chromatography on Sephadex LH 20 and quantified by GCGC recorded by a flame ionization detector. The coefficients of variation for 11 PAH range from 2.3% (BeP) to 9.4% (CHR) for a set of 5 analysis. In 1979 und 1980, 750 samples were analysed by this method.

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Profilanalyse von polycyclischen aromatischen Kohlenwasserstoffen im ng-Bereich in atmosphärischen Schwebstoffen durch Glascapillar-Gas-Chromatographie mit einem Sammelvolumen von 10 m³ Luft

Zusammenfassung Ein Verfahren wird beschrieben zur Profilanalyse von polycyclischen aromatischen Kohlenwasserstoffen (PAH) und schwefelhaltigen Analogen in atmosphärischen Schwebstoffen. Die verwendete Poly-dimethylsiloxan-phase zeigt im Temperaturprogramm (110–270° C) auch bei hoher Empfindlichkeit des FID kein Auswandern der Grundlinie.Um sekundäre Verunreinigungen der Probe während der Aufarbeitung zu vermeiden, sind besondere Maßnahmen erforderlich. Um die Expositionszeit der bereits auf dem Filter niedergeschlagenen PAH möglichst kurz zu halten, wurde die Sammelzeit auf 1 h beschränkt (10 m³/h). Eine chemische Zerstörung oder Wiederabdampfen der bereits auf dem Filter befindlichen PAH wurde durch Vergleich der PAH-Profile nach unterschiedlichen Sammelzeiten (0,5–3 h) ausgeschlossen.Der Einfluß verschiedener Lösungsmittel auf das Adsorptions-Desorptions-Gleichgewicht wurde untersucht. Die mit Toluol extrahierten PAH wurden durch eine Filtration an Silicagel und eine Chromatographie an Sephadex LH 20 gereinigt. Zur quantitativen Auswertung wurden die FID-Signale der capillar-gaschromatographisch getrennten PAH mit inneren Standard [Indeno(1,2,3-cd)fluoranthen, Picen] verglichen. Bei einer fünffachen Bestimmung liegt der Variationskoeffizient für 11 PAH zwischen 2,3% (BeP) und 9,4% (CHR). Mit der beschriebenen Methode wurden 750 Luftstaubproben ausgewertet.

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Abbreviations FLU Fluoranthene - PYR Pyrene - BNT Benzo(b)-naphtho(2,1-d)thiophene - BghiF Benzo(ghi)fluoranthene - BcPH Benzo(c)phenanthrene - BaA Benz(a)anthracene - CYC Cyclopenta(cd)pyrene - CHR Chrysene - TRI Triphenylene - BF(b+j) Benzo(b)fluoranthene, Benzo(j)fluoranthene - BkF Benzo(k)fluoranthene - BeP Benzo(e)pyrene - BaP Benzo(a)pyrene - PER Perylene - INP Indeno(1,2,3-cd)pyrene - PIC Picene (Benzo(a)chrysene) - BghiP Benzo(ghi)perylene - ANT Anthanthrene - COR Coronene - PAH Polycyclic aromatic hydrocarbons Inventory and Biological Impact of Polycyclic Carcinogens in the Environment, Part 12     

Influence of silica gel pretreatment and bonding technique on PAH selectivity of octadecyl bonded phases

Summary The effect of silica gel pretreatment and of different bonding techniques, on the chromatographic properties of octadecyl bonded phases is described. The experiments show that a monomeric octadecyl bonded phase, prepared from silica gel that has not been treated before bonding, has a poor selectivity towards polycyclic aromatic hydrocarbons (PAHs) and shows high adsorption of basic components. Silica gel treatment before the bonding of the monofunctional silane does not give a substantial improvement. Polymeric phases on the other hand show a much better PAH selectivity and a lower adsorptivity towards basic components. Further improvement can be achieved with the polymeric modification if silica gel treatment is carried out before bonding.     

Nitric acid in the presence of P2O5 supported on silica gel—a useful reagent for nitration of aromatic compounds under solvent-free conditions

A variety of aromatic compounds are nitrated to parent nitro aromatic compounds under solvent-free conditions using 65% nitric acid in the presence of P₂O₅ supported on silica gel is described. This methodology is useful for nitration of activated and deactivated aromatic rings.     

Sol–gel synthesis of mesoporous silicas containing albumin and guanidine polymers and its application to the bilirubin adsorption

The organic–inorganic composite materials based on mesoporous silica were synthesized using sol–gel method. The surface area of silicas was modified by bovine serum albumin (BSA) and guanidine polymers: polyacrylate guanidine (PAG) and polymethacrylate guanidine. The mesoporous silicas were characterized by nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, transmission electron microscopy. The obtained materials were used as adsorbents for selective bilirubin removal. It was shown that the structural properties and surface area of modified materials depend on the nature of polymers. Incorporation of polymers in silica gel matrix during sol–gel process leads to the formation of mesoporous structure with high pore diameter and a BET surface area equals to 346 m²/g for SiO₂/BSA and 160 m²/g for SiO₂/PAG. Analysis of adsorption isotherms showed that modification of silica by BSA and guanidine polymers increases its adsorption ability to bilirubin molecules. According to Langmuir model, the maximum bilirubin adsorption capacity was 1.18 mg/g.     

The influence of grafted functional groups on the adsorption properties of silica

The adsorption properties of silica gel with grafted aminopropyl and guanidinoethanethiol (GET) groups were studied by the techniques of adsorption under static conditions and gas chromatography. It was shown that molecules capable of forming hydrogen bonds are adsorbed on all modified samples more weakly than on the initial silica gel. The grafting of GET radicals on the surface results in a noticiable increase in the dispersion interaction with adsorbed molecules. Calculation of the contributions of molecular groups to the constant of adsorption equilibrium showed that the thermodynamic characteristics of adsorption on aminosilochromes and aminosilicas with a polymeric layer of the modifying agent have similar values. Such adsorbents can be used for investigation of polar compounds, including organic bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 452–457, March, 1997.     

Chromatography of Anions on Alumina Thin Layers: Effect of Transition Metals on CI−-Br−-I− and No− 2-NO− 3 Separations

Abstract

Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN)^3- ₆, Cr0₄ ^2- and Cr₂O₄ ^2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R_F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br^?, Br^?, I^? and NO^? ₂ and NO^? ₃ were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1^?-Br^?-I^? and NO^? ₂-NO^? ₃ separations has been studied.