Thermodynamics of the System HNO3-UO2(NO3)2-H2O at 298.15 K

The sorption of ⁶⁰Co, ⁶⁵Zn, ⁷⁵Se, ¹⁰³Pd, ¹¹⁰Ag and ²⁰³Hg radionuclides by polyurethane foam (PUF) was investigated and optimized with respect to the selection of appropriate sorptive medium, metal, thiocyanate ions (except for ¹¹⁰Ag) and PUF concentration and equilibration time. The influence of common anions and cations on the sorption of each metal was examined. The sorption data subjected to different sorption isotherms have shown that the sorption of all the radionuclides followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The sorption capacity intensity and energy were evaluated for each element studied. The variation of sorption with temperature was monitored for all radionuclides except zinc and selenium. The values of H, S and G were estimated and found to be negative indicating exothermic and spontaneous nature of sorption. It was found that PUF is an effective and economical sorbent for traces of metal ions which can be used for the separation/preconcentration of these ions from their very dilute solutions and has useful applications in radioanalytical and environmental chemistry and in radioactive and industrial liquid waste management.     

Determination of thermodynamic functions of sorption for cyclohexyl-, piperidyl-, morpholyl-, and thiomorpholyl-n-alkanes by capillary gas-liquid chromatography

The values of partial molar free energy (G), enthalpy (H), and entropy (S) of sorption in the homologous series ofN-alkylpiperidines,N-alkylmorpholines,N-alkyl thiomorpholines, and alkylcyclohexanes were determined. It was found that the free energy of sorption is determined to a greater extent by the enthalpy term than by the entropy one. The free energy of sorption of the first homolog decreases when then-alkyl chain is attached directly to the carbon atom of the cycle and increases in the case ofN-alkylsubstituted heterocycles. The influence of the heteroatom nature on intermolecular interactions of homologs with the nonpolar stationary phase was quantitatively estimated on the basis of thermodynamic data.Dead time necessary for calculation of the retention factor was determined by the retention of methane injected into the column simultaneously with the sample.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2030–2032, August, 1996.     

Low-Temperature Sorption–Luminescence Determination of Platinum Using Silica Chemically Modified with N-Allyl-N"-Propylthiourea and N-Phenyl-N"-Propylthiourea

Silicas chemically modified with N-allyl-N"-propylthiourea and N-phenyl-N"-propylthiourea were proposed for the low-temperature sorption–luminescence determination of platinum. The sorption of platinum(II) and platinum(IV) at the surface of sorbents yields coordination compounds luminescing at 77 K under UV irradiation. Luminescence spectra of platinum(II) complexes of thiourea derivatives covalently bonded to the silica surface exhibit a broad structureless band with a maximum at 585 nm. For the sorbent with N-allyl-N"-propylthiourea groups, the detection limit of platinum is 0.1 g per 0.1 g of the sorbent. The calibration plot is linear up to 50 g/0.1 g. The detection limit and the linearity range of calibration plots depend on the mass of the sorbent. The proposed procedure was used for the analysis of aluminoplatinum catalysts.     

A Sensitive Voltammetric Method for the Determination of Diazinon Insecticide

A sensitive voltammetric method is developed for the determination of diazinon, an organophosphorus pesticide, using a Nafion®-coated glassy carbon electrode as an enrichment film. The analysis of diazinon in aqueous solutions using sensitive instrumental methods has gained importance. Investigation of the electrochemical behavior of diazinon on a Nafion®-coated glassy carbon electrode reveals the presence of a specific oxidation peak of analytical significance. The experimental parameters, such as pH, film thickness, preconcentration potential, preconcentration time, and square-wave voltammetric parameters were optimized. Using this method, a linear calibration curve for diazinon was obtained up to 5 M range in pH 1 citrate buffer solution with a detection limit (S/N = 3) of 75 nM.     

Kinetics of the N-Monoalkylation of Aniline with Methanol Over Zn1?XCoXFe2O4 (X = 0, 0.2, 0.5, 0.8 and 1.0)-Type Systems

The kinetics of regioselective dichlorocyclopropanation of 4-vinyl-1-cyclohexene has been studied under controlled phase transfer catalysis conditions, using aqueous sodium hydroxide as the base and 2-benzylidine-N,N,N,N,N,N-hexaethylpropane-1,3-diammonium dibromide (Dq-Br) as a new phase transfer reagent. The reaction was carried out at 40 °C under pseudo-first order conditions by employing aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography. The effect of various experimental parameters on the rate of the reaction has been studied and based on the experimental results, a suitable mechanism is proposed.     

Dynamics of contact radical ion pairs C60—aromatic amines. A study by picosecond laser photolysis

Charge transfer complexes between C₆₀ and ternary aromatic amines (N,N,N,N-tetramethyl-p-phenylenediamine,p-methoxy-N,N-dimethylaniline,p-methyl-N,N-dimethylaniline,N,N-diethylaniline,N,N-dimethylaniline, and triphenylamine) were studied in chlorobenzene solutions. The lifetimes of the excited state with charge transfer in these complexes were measured by the method of picosecond laser photolysis. The dependence of the rate constant of the back electron transfer on G in the back electron transfer reaction with relaxation of the charge-transfer state exhibits the Marcus-inverted region.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1078–1089, June, 1995.The authors are grateful to D. V. Khudyakov and I. V. Rubtsov for help in experiments and to A. S. Lobach for the C₆₀ supplied.The work was financially supported by the Russian Foundation for Basic Research (Projects No. 93-03-05254 and 93-03-0217).     

A simple and robust set-up for on-column sample preconcentration – nano-liquid chromatography – electrospray ionization mass spectrometry for the analysis of<Emphasis Type="Italic"> N</Emphasis>-acylhomoserine lactones

A simple method for the simultaneous, rapid and sensitive determination of N-acylhomoserine lactone signaling molecules in bacterial isolates, without prior sample preconcentration and with minimal sample cleanup, is presented. The analysis relies on the combination of analyte preconcentration and separation on a single device: a relatively large sample volume (1–5 L) is directly loaded onto a laboratory-made, miniaturized (75 m i. d.) reverse phase nano-liquid chromatography column, connected on-line to a microelectrospray-ionization ion trap mass spectrometer. In a first step the analyte is adsorbed (and so concentrated) at the beginning of the column, and is eluted and selectively separated in a second step by the organic mobile phase. Sample preconcentration follows the mechanisms of solid phase extraction on a nano-scale, while separation takes place according to classical liquid chromatography separation principles. The columns can be manufactured easily, are simply connected, and used with minimal solvent amounts; this makes this method extremely robust and cost-effective. The analytical setup was found to be routinely quantitative down to a concentration of 10 ng/mL (corresponding to a total analyte amount of 10 pg or ca. 50 fmol). The limit of detection was reached at 1 ng/mL (1 pg, ca. 5 fmol). Compared to the classical AHL analysis of bacterial cultures with biosensors, where selectivity and sensitivity is often limited, this rapid analytical technique is a substantial qualitative and quantitative improvement. Two unsubstituted N-acylhomoserine lactones could be identified and quantified from a Burkholderia cepacia culture supernatant in a chloroform extract.     

Sorption of Mo(VI), W(VI), Cr(VI), and V(V) anions on a silica gel modified with immobilized polyionene

The sorption of polyionene 1,4-MePh on the silica gel surface was studied. The silica gel modified with polyionene sorbed was used for sorption preconcentration of MoO ₄ ^2? , WO ₄ ^2? , Cr₂O ₇ ^2? , and VO ₃ ^? anions from aqueous solutions. The sorption isotherms of these anions on the initial and modified silica gels were obtained and analyzed.     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Simple route to secondary amides of phosphorylacetic acids and their use for extraction and sorption of actinides from nitric acid solutions

An efficient method for the synthesis of secondary alkylamides of phosphorylacetic acids (APA) was proposed. The method involves amidation of ethyl phosphorylacetates with primary aliphatic amines. The scope of reaction was determined. Reactions with ethylenediamine and 1,4-diaminobutane yield the corresponding bisamides; in the case of 1,3-diaminopropane, N-(3-aminopropyl)diphenylphosphorylacetamide or N,N-propylenebis(diphenylphosphorylacetamide) was obtained, depending on the reaction conditions. The extraction of americium(III) complexes and the sorption of uranium(VI) by sorbents with physically sorbed APA from nitric acid solutions were studied. There is no correlation between the partition coefficient of americium(III) and the structure of APA; in the sorption of uranium(VI), the degree of extraction depends on the complexone structure.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2394–2402, November, 2004.     

Chromatographic Separation of Bupivacaine Enantiomers by HPLC: Parameters Estimation of Equilibrium and Mass Transfer Under Linear Conditions

Bupivacaine is an amide type local anesthetic widely used in surgery and obstetrics because of its sustained peripheral and central nerve blockade. R-(+)-bupivacaine is more toxic to the central nervous and the cardiovascular systems than S-(?)-bupivacaine. To obtain S-(?)-bupivacaine with high degree of purity using a continuous simulated moving bed (SMB) unity, equilibrium and mass transfer parameters under dilute conditions were obtained by pulse experiments using 0,0′-bis[4-terc-butyl-benzoyl]-N,N′-diallyl-L-tartar diamide immobilized in silica (Kromasil^® CHI-TBB). The linear equilibrium constants were found to be 2.12 and 2.91 for R-(+)-and S-(?)-bupivacaine, respectively. Axial dispersion coefficients were found to be practically the same for both enantiomers. A fast kinetic of mass transfer was observed. The internal resistance to the mass transfer controls all the mass transfer process in this chiral column and the pore diffusion coefficients were of the order 10^?7cm²/s. The equilibrium and mass transfer parameters will be employed in future simulation and design of operating conditions of SMB unity.     

A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g⁻¹. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L⁻¹, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples.

A schematic procedure of magnetic solid phase extraction

     

Trace metal ion preconcentration for Flame Atomic Absorption by an Immobilized N,N,N′-tri-(2-pyridyl-methyl)ethylene diamine (TriPEN) chelate ion exchanger in a flow injection system

Summary Trace Metal Ion P reconcentration for Flame Atomic Absorption by an Immobilized N,N,N-tri-(2-pyridylmetkyl)ethylene diamine (TriPEN) Chelate Ion Exchanger in a Flow Injection System Chelating groups of N,N,N-tri-(2-pyridyl-methyl)ethyIene diamine (TriPEN) were synthesized on the surface of porous glass. A 100l column of the chelate ion exchanger was incorporated into a flow injection manifold with a flame atomic absorption spectrometer. Metal ions from samples (<1 ml to>80 ml) were retained on the chelate ion exchanger until an injection of acid displaced them into the flame. A peak-shaped absorbance curve was recorded. The use of immobilized TriPEN for preconcentration of metals from dilute solution and for matrix modifications was demonstrated.     

Sorption of chromium(III) and chromium(VI) on lead sulfide

The sorption of chromium(III) and chromium(VI) on lead sulfide has been investigated in dependence on pH, time of sorption and the concentrations of sorbate and sorbent. The mechanisms of the sorption of Cr³⁺ and CrO ₄ ^2– traces on lead sulfide are discussed; a difference between CrO ₄ ^2– sorption on PbS and -Fe₂O₃ has been found. Sulfates and molybdates affect the removal of chromates from aqueous solutions. Lead sulfide carrier prepared in this work was also used for the preconcentration of chromium(III) and chromium(VI) from tap water.     

Preconcentration and Determination of Copper(II) by Novel Solid-Phase Extraction and High-Resolution Continuum Source Flame Atomic Absorption Spectrometry

Amberlite XAD-4 modified with N-para-anisidine-3,5-di-tert-butylsalicylaldimine was investigated as a new chealting sorbent for the selective separation and preconcentration of Cu(II). The metal ion was retained by chemical sorption on the modified resin, eluted by hydrochloric acid, and determined by high-resolution continuum source flame atomic absorption spectrometry. The prepared resin was characterized for the solid-phase extraction of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ in a column. The influence of the pH, the mass of solid phase, eluent, flow rate, and sample volume was optimized. Using the optimum conditions, only Cu(II) showed quantitative sorption at the 95% confidence level, and the recoveries of the other metal ions were below 80%. A preconcentration factor 125 was obtained for Cu(II) with a limit of detection of 0.56?µg?L^?1. The method was used for the determination of Cu(II) in tap water, river water, tomato leaves, and fish. The relative standard deviation and the relative error were lower than 7%.     

Quantitative determination of cationic modified polysaccharides on hair using LC–MS and LC–MS–MS

Cationic polysaccharides containing N-hydroxypropyl-N,N,N-trimethylammonium substituents are widely used as conditioning agents for hair-care products. A sensitive method has been developed for the quantitation of these polymers. After acidic extraction from hair the polysaccharides are hydrolyzed using trifluoroacetic acid. The cationic monoglycosides are determined using liquid chromatography–tandem mass spectrometry (LC–MS–MS). The developed method is independent of hair treatment. Even hair cut from test persons after customary hair wash can be analyzed. After treatment of natural and bleached hair tresses using a real-life treatment procedure 180 g and 300 g of polymer per gram hair were quantified, respectively. Additionally the fragmentation mechanism of the cationic N-hydroxypropyl-N,N,N-trimethylammonium group during electrospray ionization was investigated. A mass loss of 60 Da in combination with loss of a single charge is observed and associated with cleavage of trimethylamine and a proton. It is assumed that this process is promoted by the anionic counter-ion which might be hydroxide in an aqueous environment.     

Column preconcentration of gold by adsorbing AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> onto methyltrioctyl ammonium chloride–naphthalene and subsequent atomic absorption spectrometric determination

A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene–methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl₄^–, was retained by the adsorbent in the column at a flow rate of 1 ml min^–1. After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5–150 ng ml^–1 Au(III) with r=0.997 (n =9), and the 3 s detection limit was 0.428 ng ml^–1. The relative standard deviation for eight replicate measurements of 20 g of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.     

Cr(III) and Cr(VI) on-line preconcentration and determination with high performance flow flame emission spectrometry in natural samples

Methods for the on-line chromatographic preconcentration of Cr(III) and Cr(VI) have been developed. Cr(VI) has been preconcentrated on an RP C18 silica based column with tetrabutylammonium-bromide (TBABr) as ion-pairing agent. Specially for Cr(III) a new and effective preconcentration technique based on the sorption of Cr(III)-ions in a C18 column in presence of KH-phthalate has been developed. The efficiency of sample introduction into the atomic emission spectrometer could be improved by hydraulic high pressure nebulization. For the detection of chromium the acetylene/N₂O flame has been used as a powerful emission spectrometric source. Applying these steps the detection limit (3) could be improved to 25 pg/mL for Cr(III) and to 20 pg/mL for Cr(VI). The method has been applied for the chromium speciation in natural water samples.     

Sorption behavior of Co2+, Zn2+ and Ba2+ ions on alumina,kaolinite and magnesite

The sorption behavior of Ba²⁺, Co²⁺ and Zn²⁺ ions on alumina, kaolinite and magnesite have been investigated using the batch method.⁶⁰Co,⁶⁵Zn and¹³³Ba were used as radiotracers. The mineral samples were separated into different particle size fractions using an Andreasen Pipette. The particle sizes used in the sorption experiments were all less than 38 m. Synthetic groundwaters were used which had compositions similar to those from the regions where the minerals were recovered. The samples were shaken with a lateral shaker at 190 rpm, the phases were separated by centrifuging and adioactivity counted using a NaI(Tl) detector. Kinetic studies indicated that sorption onto the minerals took place in two stages with the slower process dominating. The highest sorption was observed on alumina. Both Freundlich and Dubinin-Radushkevich type isotherms were found to describe the sorption process well. The distribution ratio,R _d was found to be a function of the liquid volume to solid mass ratio. TheR _d 's for sorption on binary mixtures of minerals were experimentally determined and compared with those predicted fromR _d values of each individual mineral.