Measuring the electrophoretic mobility of concentrated suspensions in nonaqueous media

We present a new method of measuring the electrophoretic mobility of a particle in a concentrated suspension. The method is used to measure the electrophoretic mobility of PMMA particles (diameter 10 microm) suspended in a mixture of liquid hydrocarbons. The particle volume fraction of the suspension is varied from 0 up to 0.30 and the resulting variation of the electrophoretic mobility is discussed. The suspending liquid is such that its refractive index is very close to that of the particles. Thus the suspension is almost transparent and it is possible to follow through a microscope the motion of one particle. The suspension is subjected to a low-frequency electric field (0.5 Hz). The cell containing the suspension is mounted on a piezoelectric crystal. The displacement that compensates for the particle motion (when the particle image is steady) is determined.     

Development and validation of a gas chromatography/mass spectrometry procedure for confirmation of para-toluenesulfonamide in edible fish fillet tissue

Chloramine-T is a disinfectant being developed as a treatment for bacterial gill disease in cultured fish. As part of the drug approval process, a method is required for the confirmation of chloramine-T residues in edible fish tissue. The marker residue that will be used to determine the depletion of chloramine-T residues from the edible tissue of treated fish is para-toluenesulfonamide (p-TSA), a metabolite of chloramine-T. The development and validation of a procedure for the confirmation of p-TSA is described. Homogenized fish tissue is dried by mixing with anhydrous sodium sulfate, and the mixture is extracted with methylene chloride. The extract is passed through a silica gel solid-phase extraction column, from which p-TSA is subsequently eluted with acetonitrile. The acetonitrile extract is evaporated, and the oily residue is dissolved in hexane. The hexane solution is shaken with fresh acetonitrile. The acetonitrile solution is evaporated and the residue is redissolved in dilute potassium hydroxide solution. The aqueous solution is extracted with methylene chloride to further remove more of the fat co-extractive. The aqueous solution is reacted with pentafluorobenzyl bromide in presence of tetrabutylammonium hydrogensulfate. The resulting di-(pentafluorobenzyl) derivative of p-TSA is analyzed by gas chromatography/mass spectrometry. This method permits the confirmation of p-TSA in edible fish tissue at 20 ppb.     

Flow injection analysis of sulphite by gas-phase molecular absorption UV/VIS spectrophotometry

A flow injection gas-phase molecular absorption spectrophotometric method is described for the determination of sulphite in aqueous solution. The sulphite solution, 200 microl, is introduced into a stream of distilled water. The carrier stream containing a sulphite zone is reacted, in the first mixing coil, with a stream of sulphuric acid (1 M). The evolved sulphur dioxide is purged to the segments of nitrogen flow through the second mixing coil. The gaseous phase is separated from the liquid stream by the use of a purpose built gas-liquid separator and then is swept into a purpose built flow-through cell. The absorbance of the gaseous phase is measured at 200 nm using a UV/VIS spectrophotometer. Up to 440 microg of sulphite is determined. The limit of detection is 0.8 microg and the R.D.S. for the determination of 70 and 220 microg of sulphite are 1.02 and 0.76%, respectively. Up to 40 samples h(-1) can be analyzed. The effect of several anions and cations on the determination of sulphite was studied and the results showed that the method is relatively free from interferences. The proposed method was applied to the determination of sulphite in a synthetic sample, water sample and lemon juice.     

Development of high-temperature pulsed slit nozzle and its application to supersonic jet absorption spectrometry

A high-temperature pulsed slit nozzle, consisting of a circular pulsed nozzle and an interface to convert a circular flow into a slit flow has been constructed. The absorption spectrum is measured by scanning the wavelength of the monochromator equipped with a xenon arc lamp and by detecting the transmitted light through a jet with a photomultiplier. A rotationally cooled spectrum is clearly observed for aniline only when a long slit nozzle is employed. The absorptivity increases proportionally to the slit length at least up to 6 cm. The time for recording a spectrum is 3.5 min, which is reduced to several seconds by transmitting a white light through a jet and by measuring the spectrum with an optical multichannel analyzer. The detection limit is estimated to a partial vapor pressure of 0.4 torr for aniline. The present system can be conveniently used in routine analysis, because of a wide spectral coverage of the lamp source.     

Triglyceride determination with use of an enzyme thermistor

The application of a split-flow type of enzyme thermistor for determining triglycerides is described. The device measures the protonation heat produced when a triglyceride is passed through a column containing triacyl glycerol lipase covalently bound to controlled-pore glass beads. The time required for a determination is less than 5 min, and the calibration graph for a triolein standard is linear up to 5 mM. The procedure is used for determining triglycerides in human blood sera and is compared with a conventional spectrophotometric method.     

Numerical simulation of phase separation of immiscible polymer blends on a heterogeneously functionalized substrate

The spinodal phase decomposition of an immiscible binary polymer blend system is investigated with numerical models in two-dimensional and three-dimensional (3D). The effect of the elastic energy is included. The mechanism of the evolution of the phase separation is studied and the characteristic length R(t) is shown to be proportional to t(13). In the case when the phase separation is directed by a heterogeneously functionalized substrate, the increase in the characteristic length is divided into two stages by a critical time. The R(t) approximately t(13) diagram can be fitted with a straight line in both the first and second stages. The slope of the fitting line significantly decreases after the critical time. The compatibility of the resulting pattern to the substrate pattern is also measured by a factor C(S). It is observed that there is also a critical time in the evolution of the compatibility for the cases with and without elastic energy. The critical time of C(S) is identical with the respective critical time of R(t). The lateral and vertical composition profiles functionalized substrate is observed with the 3D model. The difference mechanism of the cases with and without elastic energy is discussed.     

An automated submicrogram determination of selenium in vegetation by quartz-tube furnace atomic-absorption spectrophotometry

An automated method for the determination of submicrogram amounts of selenium in vegetation is described. A weighed sample of vegetation is digested with a 4:1 nitric-perchloric acid mixture, and made up to a known volume. The digested sample is placed in a Technicon sampler and reacted with sodium borohydride solution. The selenium converted into the gaseous hydride is swept by an argon stream into a gas-liquid separator. The mixed gas stream is passed through a heated quartz cell, positioned in the light-path of an atomic-absorption spectrophotometer. The absorption by the atomized selenium is recorded. The method is capable of analysing 50 samples a day by the use of a calibration curve or 25 a day by the standard addition technique. A relative standard deviation of better than 10% and a detection limit of 0.025 microg/g were obtained.     

Experimental investigation of contact angle, curvature, and contact line motion in dropwise condensation and evaporation

Image-analyzing interferometry is used to measure the apparent contact angle and the curvature of a drop and a meniscus during condensation and evaporation processes in a constrained vapor bubble (CVB) cell. The apparent contact angle is found to be a function of the interfacial mass flux. The interfacial velocity for the drop during condensation and evaporation is a function of the apparent contact angle and the rate of change of radius of curvature. The dependence of velocity on the apparent contact angle is consistent with Tanner's scaling equation. The results support the hypothesis that evaporation/condensation is an important factor in contact line motion. The main purpose of this article is to present the experimental technique and the data. The equilibrium contact angle for the drop is found experimentally to be higher than that for the corner meniscus. The contact angle is a function of the stress field in the fluid. The equilibrium contact angle is related to the thickness of the thin adsorbed film in the microscopic region and depends on the characteristics of the microscopic region. The excess interfacial free energy and temperature jump were used to calculate the equilibrium thickness of the thin adsorbed film in the microscopic region.     

Substoichiometric isotope dilution analysis for uranium by synergic extraction

Substoichiometric extraction of uranyl ion in a synergic system of a chelating reagent and a neutral ligand is described. The system is based on a substoichiometric amount of 2-thenoyltrifluoroacetone (TTA) and an excess of tributylphosphate (TBP); this is compared with a system involving a substoichiometric amount of trioctylphosphine oxide and an excess of TTA. The reproducibility of the substoichiometric extraction is 0.46 or 0.62%, respectively. The former method is superior because extraction of uranyl ion with TBP alone is negligible. The method is applicable to > ca. 10 μg of uranium.     

Die Tautomeriegleichgewichte von Dihydrochinoxalinen

The primary product of the two step reduction of 2-phenylquinoxaline is the 1,4-dihydrocompound which undergoes a tautomeric rearrangement to the thermodynamically more stable 1,2-dihydro-3-phenylquinoxaline. The 1,4-dihydro compound is an extremely reactive reducing agent whereas the 1,2-dihydro form is almost inert against oxidizing agents. Both dihydro forms are in a kinetically hindered equilibrium. The rearrangement requires a transfer of a proton from a nitrogen to a carbon atom and is therefore relatively slow even at pH 0. The 1,2-dihydro compound cannot take part in redox reactions directly. If this compound is oxidized, the rate determining step is always the reversed tautomeric rearrangement. The effect of the kinetics of the tautomeric rearrangement on the polarographic behavior of the 2-phenylquinoxaline system is discussed.     

Predictions from the trigger mechanism for Ziegler-Natta polymerization of α-olefins

The trigger mechanism is a new concept for understanding the polymerization of α-olefins with Ziegler-Natta catalysts. The mechanism is based on the interaction of two monomers in the transition state, where an incoming monomer triggers the insertion of a complexated monomer. The monomer site is never a free site, and is thus protected from attack by Lewis bases in the reaction medium. The stereochemical discrimination is due to the interaction of the two monomers. This interaction determines the orientation of the incoming monomer, and the stereochemistry of the insertion is given when the monomer is complexated. The model predicts a reaction rate order vs. monomer concentration between 1.0 and 2.0, a reduced overall polymerization rate above a given temperature, very complex kinetics for copolymerization, a lower stereochemical discrimination for the first inserted monomer, and a high stereochemical discrimination.     

Role of the cure kinetics in morphology control at phase separation of curing multicomponent thermosets and a criterion of equilibrium

The formation of heterophase polymers via phase separation in the course of curing reaction in a blend of a thermosetting oligomer with a rubber modifier is considered. The interference of thermodynamic and kinetic factors that define the morphology of the material being formed is discussed. The need for a kinetic theory of cure-induced phase separation is established, and an approach of this kind is proposed. On the basis of this approach a simple quantitative criterion of deflection of the phase-separating system from the thermodynamic equilibrium is given.     

An ATR method for measurement of IR circular dichroic spectra

The present study is an attempt to obtain circular dichroic IR spectra using a conventional ATR attachment provided with a hemicylinder of a high enough refractive index. The measurement is carried out by means of FTIR spectrometers taking a difference spectrum from two ATR experiments. The first one is performed with linearly polarized light of a suitable azimuth while the same azimuth but of opposite sign is used for the second experiment. A theoretical treatment is presented.     

Atomic charges based on spherical harmonics expansion at the atomic centers

Molecular orbitals are expanded in spherical harmonics functions around atomic centers. The expansion coefficient is a function of the distance from the nucleus and the quotient between this function and a corresponding atomic orbital is almost constant in the core region. The square of the quotient is used as a definition of an atomic charge component. The erratic dependence on the type of basis functions in the Mulliken method is thereby avoided. The relationship between the new charge and the Mulliken population is investigated and a new invariant Mulliken population is suggested.     

A simple optical device for measuring free surface deformations of nontransparent liquids

In this paper, a novel optical device for measuring the deformation of liquid free surfaces is presented. The device employs a laser beam, which can be focused on any chosen location on the free surface. The key measurement is of the intensity of the beam reflected from a location on the free surface where the deformation exhibits a local extremum. The optics of the device is so designed as to measure a maximum intensity when the distance between the focusing lens and the selected point on the free surface is equal to the focal length, thus enabling a height measurement. The device is tested in ferrofluid pools where the height of the spikes of the normal field instability is measured. The simplicity of the suggested technique enables the fabrication of a quite cheap device for measuring surface deformation of nontransparent liquids, which provides good accuracy and reproducibility.     

The passive DC conductivity of human tissues described by cells in solution

The electrical conductivity of human tissue at low frequencies is discussed when a uniform electric field is applied to some tissue containing many cells. Human tissue is described as a suspension of particles in a conducting solution. Relations are derived for the apparent conductivity of a cell surrounded by a membrane. These relations can be used to estimate the accuracy of a model that considers the cell as a non-conducting particle. Usually, a tissue is composed of several types of particles. A relationship that expresses the effective conductivity of a suspension of one type of ellipsoidal particles could be found in the literature. The orientation of the particles could be uniform or they could be randomly distributed. For non-conducting particles, this expression is known as Archie's law. The expression is extended such that also the effective conductivity of a suspension of various types of particles can be calculated. The result is evaluated for the cortex of the brain using experimental data given in the literature.     

Fabrication of a Simple and Cheap Screen-printed Silver/Silver Chloride (Ag/AgCl) Quasi-reference Electrode

In this work, a silver/silver chloride ink is fabricated using two steps. First the silver ink is prepare using silver, nail polish and acetone. Then the silver ink is painted in a paper substrate and a silver chloride layer is deposited using a bleach solution. The result is the silver/silver chloride conductive ink. The silver ink is cheap ($2.49/g), well-dispersive and very easy to fabricate. The materials were characterized by SEM and XRD. The Ag ink showed the formation of a continuous network throughout the silver ink film with fewer agglomeration. The effective chlorination process was also observed in the Ag/AgCl characterization. Since the Ag/AgCl substrate will be used as a quasi-reference electrode, it is important to investigate the electrical properties. The Ag ink showed an average ohmic resistance of 2.27 Ω. The addition of the AgCl layer decreases the conductivity, as expected. In summary, the Ag/Ag/Cl ink developed is simple, well-dispersed, cheap and with good conductivity. Therefore, it can be used as a conductive ink in the fabrication of quasi-reference electrodes.     

A lubricated stagnation point flow of nanofluid with heat and mass transfer phenomenon: Significance to hydraulic systems

The improved thermal association of heat transfer is considerably observed due to interaction of nanoparticles in recent days. The lubrication phenomenon with heat and mass transfer effects plays a key role in the hydraulic systems. In current research, the thermal impact of nanofluid over a lubricated stretching surfaces near a stagnation point analytical has been studied. A thin layer of lubricating fluid with a variable thickness provides lubrication. The inspection of thermophoresis and Brownian motion phenomenon is illustrated via Boungrino model. The analytical finding of refurbished boundary layer ordinary differential equations is obtained by a reliable and proficient technique namely variational iteration method (VIM). The Lagrange Multiplier is a potent tool in proposed technique to reduce the computational work. In addition, a numerical comparison is presented to show the effectiveness of this study. The range of flow parameters is based on theoretical flow assumptions. Physical inspection of involved parameters on velocities, temperatures, concentrations, and other quantities of interest when lubrication is presented. The current results present applications in polymer process, manufacturing systems, heat transfer and hydraulic systems.     

A software package for the evaluation of peak parameters in an analytical signal based on a non-linear regression method

Computer-based data handling of analytical signals to extract commonly used analytical parameters often produces poor results if the signals are affected by noise and a drifting baseline. Only a minor part of the information present in the signal is used for correction. A computer package is presented, in which the total information of the signal is used to give accurate evaluation of analytical parameters. The program uses a non-linear regression method to deconvolute analytical signals into a number of peaks and a baseline. To describe the peak shape any mathematical model can be used. In the computer package, a Gaussian curve-related model is used, with variable asymmetry. The baseline is described with a polynomial of variable order. The method is simultaneously a filter procedure Deconvolution of poorly separated peaks is possible. The software is developed on a minicomputer; however, test results of this study indicate the feasibility of implementation on a microcomputer without extremely time-consuming runs of the program.     

A specific bio-electrochemical sensor for hydrogen peroxide

A bio-electrochemical sensor specific for hydrogen peroxide is described. The sensor consists of two membranes—a catalase-collagen membrane and a teflon membrane—an alkaline solution, a platinum cathode and a lead anode. The catalase-collagen membrane is prepared electrochemically, the thickness being 1 μ; the enzyme activity is similar to that of native catalase. The sensor responds to hydrogen peroxide with a response time of only 1–2 min. The calibration curve is quite linear over a concentration range of 0–1.5 mmol l^-1 for hydrogen peroxide. The utility of the sensor in continuous usage is discussed.