Direct determination of copper in urine using a sol–gel optical sensor coupled to a multicommutated flow system

In this work, a multicommutated flow system incorporating a sol–gel optical sensor is proposed for direct spectrophotometric determination of Cu(II) in urine. The optical sensor was developed by physical entrapment of 4-(2-pyridylazo)resorcinol (PAR) in sol–gel thin films by means of a base-catalysed process. The immobilised PAR formed a red 2:1 complex with Cu(II) with maximum absorbance at 500 nm. Optical transduction was based on a dual-colour light-emitting diode (LED) (green/red) light source and a photodiode detector. The sensor had optimum response and good selectivity towards Cu(II) at pH 7.0 and its regeneration was accomplished with picolinic acid. Linear response was obtained for Cu(II) concentrations between 5.0 and 80.0 g L^–1, with a detection limit of 3.0 g L^–1 and sampling frequency of 14 samples h^–1. Interference from foreign ions was studied at a 10:1 (w/w) ion:Cu(II) ratio. Results obtained from analysis of urine samples were in very good agreement with those obtained by inductively coupled plasma mass spectrometry (ICP–MS); there was no significant differences at a confidence level of 95%.     

Silica Gels and Gel Glasses Containing Silver and Platinum Metal Particles

Silica gels containing between 0.05 and 20.0 mol% Ag2O and between 0.1 and 1.0 mol% PtO2 have been synthesized using TEOS, C2H5OH, H2O, HNO3, HCl, AgNO3 and PtCl4 as precursors. The gels obtained with Ag2O are colorless, while the gels containing PtO2 are yellow. The gels have been heat treated in the 25–1000°C temperature range. The processes of structural evolution of gels have been studied by means of IR-spectroscopy, X-ray diffraction analysis, transmission electron microscopy (TEM) and transmission electron microdiffraction (TEMD). It has been established that the temperature of gel to gel-glass transition decreases when the Ag2O content of the gels increases. The same tendency was established for the gel to gel-glass transition in the SiO2-PtO2 system.Special attention was paid to the formation of silver and platinum metallic particles in amorphous materials. The microstructure of the gels has been observed and the sizes of the metal particles were determined to be from 3 to 25 nm.The crystallization processes in the gels heat treated at 1000–1200°C have been examined and besides the silver and platinum particles -cristobalite was formed.It has been shown that nanocomposite materials containing ultrafine silver and platinum particles in SiO2 amorphous or polycrystalline matrixes can be obtained.     

Conductivity and Electrokinetic Potential of Microcrystalline Cellulose Particles in Aqueous HCl and NaOH Solutions

The conductivity of microcrystalline cellulose (MCC) dispersions in aqueous 10^–5–10^–2 M HCl and NaOH solutions was measured as a function of the particle volume fraction by the conductometry. The dependence of the relative conductivity of MCC particles on pH of equilibrium solutions was determined using the Wagner equation. The electrophoretic mobility of MCC particles in the aforementioned solutions was measured by the microelectrophoresis, and corresponding dependences of the particle potentials on pH of aqueous HCl and NaOH solutions (pH 2–11) were calculated using the Smoluchowski and Henry equations of the electrophoresis theory. It was shown that, in the case of MCC, the Henry equation, which allows for the significant conductivity of the dispersed particles, as compared with the dispersion medium, makes it possible to calculate more accurate potential values and, consequently, to derive the (pH) dependence, which is satisfactorily consistent with the effect of the surface charge and solution ionic strength on the potential in a wide pH range.     

Optical detection and discrimination of cystic fibrosis-related genetic mutations using oligonucleotide–nanoparticle conjugates

Novel methods for application of oligonucleotide–gold nanoparticle conjugates to selective colorimetric detection and discrimination of cystic fibrosis (CF) related genetic mutations in model oligonucleotide systems are presented. Three-strand oligonucleotide complexes are employed, wherein two probe oligonucleotide–gold nanoparticle conjugates are linked together by a third target oligonucleotide strand bearing the CF-related mutation(s). By monitoring the temperature dependence of the optical properties of the complexes, either in solution or on silica gel plates, melting behaviors may be accurately and reproducibly compared. Using this approach, fully complementary sequences are successfully distinguished from mismatched sequences, with single base mismatch resolution, for F 508, M470V, R74W and R75Q mutations.     

The determining role of three-phase contact mobility and contact angle magnitude in the selectivity of a flotation process

The following two cases of attachment of particles onto the water-air interface are considered: a) perfectly sliding three-phase contact, according to Nutt and b) three-phase contact of very strong hysteresis or detachment throught a neck. The corresponding expression relating the contact angle, mobility of the three-phase contact, the radius of the particles and the flotation selectivity parameter are obtained. Experimental data for the systems: for quartz-galena 10^–5 M/1 solution of potassium ethylxanthogenate and for glass spheres 10^–5 M/1 solution of dodcylamoniumchloride are presented. Particles in the range of radii from 10^–5 to 10^–5 cm are considered.The present study indicates a possibility to enhance flotation selectivity through the appropriate classification of initial material and/or collective concentrates, and separate flotation of the different size ranges. At some size ranges selectivity will be enhanced while at others the flotation process will be intensified.     

Effect of Fluorine Doping on Semiconductor to Metal-Like Transition and Optical Properties of Cadmium Oxide Thin Films Deposited by Sol–Gel Process

Highly conducting fluorine doped n-type cadmium oxide thin films have been synthesized by sol–gel dip coating process on glass and Si substrates for various fluorine concentrations in the films. X-ray diffraction pattern confirmed the cubic CdO phase formation and SEM micrograph showed fine particles of CdO with size ~0.3 m. F concentration in the films was varied from 1.8% to 18.7% as determined from energy dispersive X-ray analysis (EDX). The resistivity of the CdO films decreased with increase of F doping and increase of temperature below 14.6% of F, as usual for semiconductors. Above this F concentration the resistivity increased with increase of temperature like metals. Hall measurement showed very high carrier concentrations in the films lying in the range of ~2.93 × 10²⁰ cm^–3 to 4.56 × 10²¹ cm^–3. UV-VIS-NIR spectrum of the films showed the optical bandgap energy increased with increase of F doping and corresponding carrier concentrations obtained from Burstein-Moss shift also support the Hall measurement results.     

Auto-Organisation in Silica-Based Organic-Inorganic Gels Obtained by Sol-Gel Process

A new type of hybrid material is prepared through sol-gel processing by the polycondensation of (MeO)₃Si–R–Si(OMe)₃ units containing a rigid organic anisotropic group R. The hybrid covalently bounded organic-inorganic gel shows an unexpected structural birefringence n (n = 2 × 10^–3). This birefringence is induced by a strain field anisotropy during gel aging as revealed by simultaneous dynamic light scattering and birefringence measurements. To better address the role of the strain field, we use a free interface sol-gel/air to control strain anisotropy and to measure the gel optical axis and its birefringence. We find that the birefringence is associated to a long-range orientational order of organic moieties induced by the strain anisotropy during the gel aging.     

1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.     

A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

Exciton Chirality Method. Oriented Molecules – Anisotropic Phases

The results of the theory of the anisotropy of optical activity (ACD), especially of the circular dichroism (CD), in view of its application to the exciton chirality method was presented. In order to introduce the phenomenology some typical experimental anisotropy effects of the ACD of a dibenzoate and two taddoles were discussed. The CD and ACD of unbridged and bridged 1,1-binaphthols were described taking into account results of the polarized spectroscopy. Their CD and ACD spectra were decomposed into contributions of their two exciton transitions. It was proven that the electric dipole/electric quadrupole transition moments contribute in same order of magnitude as the electric dipole/magnetic dipole transition moments to the tensor coordinates of the CD tensor for a bridged 1,1-binaphthol. The CD tensor coordinates _ii^* for a light beam propagation along the principal axes of the order tensor of a 1,1-binaphthol of approximately C₂ symmetry are very different in size and also of different sign. The largest tensor coordinate belongs to the direction along the naphthyl–naphthyl bond. The CD along the C₂ symmetry axis is approximately zero. The CD tensor coordinates of different sign along different directions within a molecule can be assigned to different helicities in their molecular structure along these directions. For (R)-1,1-binaphthol skeleton the left handed helix along an axis, which is perpendicular to the naphthyl–naphthyl bond and perpendicular to the C₂ symmetry axis, leads to a positive couplet whereas for the right-handed helix along the naphthyl–naphthyl bond a negative couplet has been found. Thus, the ACD with its determination of the _ii^* allows to observe different helicities along different directions within a molecule. As well for the bridged as the unbridged binaphthols in the spectral region of the exciton bands a third transition not belonging to the exciton band system was detected.     

Intermittent stirring: A method for achieving equilibrium in adsorption systems with a solid phase sensitive to the breakdown of particles

The method of agitation has a great influence on the kinetics of adsorption of cobalt by synthetic geothite /-FeOOH/ suspended in 10^–2 mol l^–1 NaCl at pH 7. Three methods of agitation were compared, reciprocating shaking, continuous stirring and intermittent stirring, and only with the latter was equilibrium achieved. This suggests that in sorption systems with a solid phase subject to aggregation of particles the breakdown of aggregates can be prevented by intermittent stirring.     

Fluorescence and Absorption Probe of Metal Ion Centers in Silicates Obtained by the Sol-Gel Technique

An optical probe of the structure of metal ion centers in sol-gel systems based on Eu3+ and Nd3+ emission and absorption measurements has been developed. The effects of the structure and composition of organic complexes of Eu3+ on the clustering processes and retention of water molecules in the gel and glasses were investigated. Mechanical properties of systems prepared with Triton detergent were also investigated. The studies have been performed for two types of complexes of lanthanides, with -diketones as the precursor lanthanide salts. The emission, excitation and absorption spectra of the precursor salts, gels and glasses heated to 1100 K were measured. Splitting of the levels and electronic transition probabilities were analyzed. The IR spectra were used for the detection of the OH– modes in the glasses.     

Analytical possibilities of microelectrode use for stripping voltammetry

The analytical utility of microelectrodes for stripping voltammetry is discussed from several points of view. The application of microelectrodes for microanalysis is demonstrated using a novel capillary flow injection system. Heavy metals at g l^–1 concentrations have been determined in l-samples. The influence of electrode size and convection during the deposition period of anodic stripping voltammetry on the reproducibility of trace metal determination was studied for various types of electrodes. In the case of mercury film microelectrodes, the precision can be improved if the accumulation of the analyte is performed under quiescent conditions. Practical examples of stripping voltammetry with microelectrodes such as copper determination in whisky and trace metal measurements in drinking water are given.     

Diffusing-particle trapping kinetics for a one-dimensional solution

Solvent components that prevent reagent diffusion lead to a proportion of particles that do not react, which affects the decay in the reagent concentrations. The A+ BB reaction occurring in a one-dimensional system may be accelerated or retarded in accordance with the solvent concentration. Experiments are indicated in which it is predicted that one can observe effects from fluctuations in the concentrations of the B particles and solvent components.Translated from Teoreticheskaya i éksperimental'nana Khimiya, Vol. 24, No. 1, pp. 8–13, January–February, 1988.     

An Electrochemical Sol–Gel Sensor for Determining Iron by Stripping Voltammetry

Electrochemical sensors were developed based on thick-film carbon-containing electrodes coated with thin xerogel films fabricated by the sol–gel technology. The effect of the composition of a hydrolyzed mixture and the types of carbon-containing inks and a support on the properties of sol–gel electrodes was studied. Conditions for preparing sol–gel film sensors modified with 1,10-phenanthroline, 2,2-dipyridyl, Chrome Azurol S, and Eriochrome Cyanine were chosen, and the electrochemical properties of these sensors were studied. Optimum conditions are found for determining total iron by stripping voltammetry (SVA) using sol–gel sensors modified with 1,10-phenanthroline and 2,2-dipyridyl. The detection limit for iron(II, III) was found to be 0.02 mg/L at an accumulation time of 60 s. The sol–gel sensors were used in the analysis of natural waters.     

Silicon-containing polymers for non-linear optics

A variety of novel poly[ethynediyl-arylidene-ethynediyl-silylene]s (PEAES), including those containing hypercoordinate silicon atom as well as donor and acceptor groups, has been synthesized. The presence of hypercoordinate silicon favours high values of fast Kerr-type non-linearities, and the incorporation of amide groups gives rise to good optical quality nanocomposites in a silica matrix. The inorganic-organic hybrid sol-gel film incorporating 5–14 mass% of the polymer containing pentacoordinate silicon showed Re ⁽³⁾ = –9.5 ×10^–11 esu. The predominant rôle of the electron nonlinear mechanism has been demonstrated by using test beams with linear and circular polarizations. The photorefractive properties of composites based on PEAES as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm without preliminary electric poling. The photorefractive origin of the refractive index changes was confirmed by the high two-beam gain under an externally applied electric field. Refractive index gratings affording two-beam gain can also be written under zero field conditions. To explain this unique property of the materials it is suggested that chromophore orientation asymmetry arises either during film formation or is induced by the longitudinal intensity gradient.     

IR spectroscopic study of the conformational lability of 4′-ethyl-4-cyanobiphenyl

The conformational lability of 4-ethyl-4-cyanobiphenyl molecules in solid crystal (SC) and isotropic liquid (IL) states was investigated by IR spectroscopic techniques (experiment and theory). IR absorption spectra were measured at 28°C–95°C in the frequency range 400 cm^–1–4000 cm^–1. Spectrum simulation was performed using the fragment method with allowance for the conformational fluctuations of molecules. The experimental and calculated spectra were compared and analyzed, and it was shown that in the IL, the samples are mixtures of conformers. The temperature changes in the spectra in the stated range are caused by the conformational lability of molecules.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Raman-spectrophotometric determination of the tungstate anion and its isopolyanions in aqueous systems

Summary The tungstate and some isopolyanions were determined by Raman spectrophotometry. Using the more intensive Raman active vibrational bands of these species and the bending vibration of water at 1,650 cm^–1 as an internal standard the linear ranges for the measurement of concentrations were elucidated. The detection limits for tungstate, paratungstate-A, -metatungstate and metatungstate are 4×10^–3 M, 9×10^–3 M, 10^–2 M and 10^–2 M, respectively. This technique was used to examine a mixture of tungstate and paratungstate-A.

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Raman-Spektrophotometrische Bestimmung des Wolframat-Anions und seiner Isopolyanionen in wäßrigen Systemen

Zusammenfassung Die intensiveren Raman-aktiven Schwingungen dieser Ionen gestatten die Erstellung linearer Eichfunktionen, wobei die Deformationsschwingung des Wassers bei 1650cm^–1 als interner Standard herangezogen wird. Die Nachweisgrenzen liegen bei 4·10^–3 M für das Wolframat, 9·10^–3 M für das Parawolframat-A und 10^–2 M für -Meta- sowie Metawolframat. Das Verfahren wird zur Bestimmung von nebeneinander vorliegenden Wolframat- und Parawolframat-A-Anionen verwendet.

     

Rheological properties of filled gels. Influence of filler matrix interaction

The dynamic moduli of gels filled with particles have been studied as a function of the volume fraction of dispersed particles _f (0–0.4) and of the way in which they interact with the gel matrix. Two gels of different nature were studied, viz. polyvinyl alcohol (PVA) — Congo red gels (a so-called rubber gel) and casein gels made by acidification of skimmed milk. Emulsion droplets stabilized by different macromolecules have been used as dispersed particles. If there was no interaction between the macromolecules adsorbed on the particles and the gel matrix, both the filled PVA and the filled casein gels showed a small decrease in the elastic moduli with _f , approaching the behaviour theoretically predicted for foams. In the case of interaction, the results for filled PVA gels roughly fitted the theoretical predictions, if the deformability of the emulsion droplets and the formation of an intermediate layer between the dispersed particles and the gel matrix was taken into account. The increase in the elastic moduli of the acid milk gels with _f was much greater than expected and was probably due to aggregation of the dispersed particles during gelation.     

Radiolytic gas formation under γ-irradiation of oxalic acid solutions

Radiolytic gas formation under -irradiation (10⁴–10⁶ Gy) of 10^–2–10^–4 M aqueous solutions of oxalic acid at 25–60°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1836–1839.Original Russian Text Copyright © 2004 by Popova, Voronin, Byvsheva.