Combined Analytical Method Research Articles

Coupling of headspace solid phase microextraction with ultrasonic extraction for the determination of chlorinated pesticides in bird livers using gas chromatography

In the present study a combined analytical method involving ultrasonic extraction (USE), sulfuric acid clean-up and headspace solid-phase microextraction (HS-SPME) was developed for the determination of chlorinated pesticides (CPs) in bird livers. Extraction of CPs from 1 g of liver was performed by ultrasonication for 30 min using 20 mL of solvent mixture (n-hexane:acetone (4:1, v/v)). The extract was subsequently subjected to a clean-up step for lipid removal. A comparative study on several clean-up procedures prior to the HS-SPME enrichment step was performed in order to achieve maximum recovery and optimal clean-up efficiency, which would provide suitable limits of detection in the gas chromatographic analysis. For this purpose, destructive (sulfuric acid or sodium hydroxide treatment) and non-destructive (alumina column) clean-up procedures has been assayed. The treatment of the extract with 40% (v/v) H 2SO 4 prior to HS-SPME process showed the best performance since lower detection limits and higher extraction efficiencies were obtained. The method detection limit ranged from 0.5 to 1.0 ng g −1 wet weight and peak areas were proportional to analyte concentrations ( r 2 > 0.990) in the range of 5–500 ng g −1 wet wt. The method was found to be reproducible (R.S.D. < 10%) and effective under the operational conditions proposed and was applied successfully to the analysis of CPs in liver tissues of various bird species from Greece.

Computation of the no-load voltage waveform of laminated salient-pole synchronous generators

This paper presents a combined analytical and finite-element (FE) method for computation of the no-load voltage waveform of laminated salient-pole synchronous generators. The described method takes into account saturation effects as well as the damper bar currents due to the slot pulsation field. The method calculates first the damper bar currents and then includes them in the calculation of the no-load voltage. The combination of magnetostatic two-dimensional (2-D) FE simulations for calculating the magnetic coupling between the machine windings and of an analytical resolution results in a very precise prediction of the no-load voltage. At the same time, simulation time is drastically reduced compared with transient magnetic 2-D FE simulations. The method was verified on several examples, comparing the obtained results (damper bar currents and no-load voltage) with results obtained from transient magnetic FE simulations and, in one case, with the measured no-load voltage.

Evaluation of Tritium Behavior in the Epoxy Painted Concrete Wall of ITER Hot Cell

Tritium behavior released in the ITER hot cell has been investigated numerically using a combined analytical methods of a tritium transport analysis in the multi-layer wall (concrete and epoxy paint) with the one dimensional diffusion model and a tritium concentration analysis in the hot cell with the complete mixing model by the ventilation. As the results, it is revealed that tritium concentration decay and permeation issues are not serious problem in a viewpoint of safety, since it is expected that tritium concentration in the hot cell decrease rapidly within several days just after removing the tritium release source, and tritium permeation through the epoxy painted concrete wall will be negligible as long as the averaged realistic diffusion coefficient is ensured in the concrete wall. It is also revealed that the epoxy paint on the concrete wall prevents the tritium inventory increase in the concrete wall greatly (two orders of magnitudes), but still, the inventory in the wall is estimated to reach about 0.1 PBq for 20 years operation.

On the methodology for integration of traditional Chinese and Western medicine

Traditional Chinese medicine and modern Western medicine have their distinctive superiorities, and are mutually complementary in spite of their different systems of theory. The integration of traditional Chinese medicine and modern Western medicine can promote the development of medical science. Over the past 40 years, a number of great achievements have been made in the field of the integration, promoting the development of medicine in China. To sum up in respect of methodology, these achievements are obtained by application of combined analytical and synthetical methods of modern medicine to the research of basic principles, therapeutic methods, prescription and medication of traditional Chinese medicine.

Determination of the elemental composition of cyanobacteria cells and cell fractions by atomic emission and atomic absorption spectrometry

An approach to studying the elemental composition of cyanobacteria Spirulina platensis and Nostoc commune using a set of complementary analytical methods (ICP-AES, PAAS, and ETAAS) is proposed. The procedures were adapted for the determination of macro- and microelements (Na, K, Mg, Ca, Fe, Mn, Cu, Mo, Zn, B, and Se) in the biomass of cyanobacteria and separated cell fractions (chloroform and water-methanol extracts and precipitates). The conditions for the mineralization of biological materials were optimized for autoclave and microwave sample preparation procedures. The evaporation and atomization of Se and Mo in a graphite furnace in the presence of chloroform and methanol were studied. The use of combined analytical methods and the interpretation of analytical results allow one to draw conclusions about the ability of cyanobacteria to accumulate biologically important microelements (B, Mo, Se, and Zn) and to optimize technological processes for manufacturing biologically active substances.

A direct determination of weight functions for arbitrary three-dimensional cracks – a combined analytical and numerical approach

A combined analytical and numerical method is proposed for the determination of the weight functions of stress intensity factors of cracks in an arbitrary three-dimensional elastic body. Having defined the weight functions for a given geometry of a structure, the stress intensity factors for arbitrary loading conditions can be obtained by a simple inner product of the weight function and a traction vector. Traditionally weight functions are defined in the two ways; the one is defined by the hyper-singular term of the eigen-function expansion of the displacement field of a cracked body, and the other is defined by the variation of displacement field with respect to a virtual extension of a crack. In the present paper, the weight functions for stress intensity factors are defined by applying the Maxwell-Betti's reciprocal theorem to an original problem and the auxiliary problems subjected to three kinds of force-couples acting on the crack surfaces near the limiting periphery of an arbitrary three-dimensional crack. In the present formulation, weight functions can be calculated by using a general-purpose finite element code combined with analytical expressions near the condensation point, where hyper-singularities exist. The validity of the method is confirmed by two- and three-dimensional illustrative examples.

Pinched inlet split flow thin fractionation for continuous particle fractionation: application to marine sediments for size-dependent analysis of PCDD/Fs and metals.

It is demonstrated that split-flow thin (SPLITT) fractionation, a continuous separation technique for sorting particles or macromolecules, can be utilized for the fractionation of environmental particles to study a size-dependent analysis of pollutants. In this study, focuses are made on the use of a pinched inlet gravitational SPLITT fractionation, a modified form of SPLITT channel formed by reducing the sample inlet thickness of the channel to improve separation efficiency, to separate marine sediments into five different sizes (<1.0, approximately 1.0 to 2.5, approximately 2.5 to 5.0, approximately 5.0 to 10, and approximately 10 to 53 microm). The resulting size fractions are examined with high resolution gas chromatography/high resolution mass spectrometry to determine the size-dependent distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans along with a statistical data treatment and are analyzed with inductively coupled plasma-atomic emission spectrometry and graphite furnace atomic absorption spectrometry to ascertain its major and trace metals. It is shown that the combined analytical methods detailed in this study can be powerfully utilized in such a way as to analyze pollutant distribution and its concentration with regard to particle sizes for an environmental assessment.

Mode-II Fatigue Fracture of Wood-Composite Bonded Interfaces

In this paper, the shear mode (mode-II) fatigue fracture of wood-FRP bonded interfaces using a unique linear tapered end-notched flexure (TENF) specimen is presented. A tapered beam on elastic foundation (TBEF) model developed for design and analysis of the TENF specimens is first reviewed. A combined analytical and experimental fracture mechanics method is developed to evaluate the fatigue fracture behavior of wood-FRP bonded interfaces under mode-II constant cyclic loading conditions. By applying the compliance method with the unique feature of TENF specimen (i.e., a constant compliance rate change) and modifying the original Paris Law equation, the fatigue fracture behavior of wood- FRP interface under Mode-II loading is effectively evaluated. The possible effects of loading variables (i.e., load ratio, waveform, and frequency) on crack propagation rate are investigated. Both the load ratio and frequency have shown pronounced influences on crack propagation rate; while the waveform has negligible effect. A modified Paris Law equation is proposed to include both the frequency and load ratio effects. The present method can be used for other similar studies of interface fracture of dissimilar materials, and the finding of this study can eventually lead to the development of design guidelines for hybrid material bonded interface.

A COMBINED ANALYTIC AND NUMERICAL METHOD FOR PREDICTING THE SOLID-LAYER GROWTH FROM MELT CRYSTALLIZATION

The kinetics of crystallization limit the rate in which crystal growth can occur without in-corporation of undesired impurity. If the rate of heat transfer exceeds the mass transfer rate of the inpurity, the impurity can solidify, contaminating the product. One would like to specify a rate of crystallization and determine the temperature profile of the crystallizer wall that would achieve this result. This is an inverse problem that has not been solved in the previous crystallizer models. A combined analytic and numerical method for solving the inverse problem is given in this article. The method is illustrated by an example.

First 2-Hydroxy-3-Methylbut-3-Enyl Substituted Xanthones Isolated From Plants: Structure Elucidation, Synthesis and Antifungal Activity

Two new 2-hydroxy-3-methylbut-3-enyl substituted xanthones, ( - )-caledol 1 and ( - )-dicaledol 2 were isolated from a dichloromethane extract of the leaves of Calophyllum caledonicum (Clusiaceae). Compounds 1 and 2 are the first 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from natural source. Their structures were elucidated by means of combined analytical methods including HRFABMS, 1D and 2D NMR spectroscopies and also confirmed by total synthesis using biomimetic ortho -prenylphenols photooxygenation ( 1 O 2 ) as a key step. The antifungal activity against Aspergillus fumigatus is reported.

Continuous fractionation of fly ash particles by SPUTT for the investigation of PCDD/Fs levels in different sizes of insoluble particles.

A combined analytical method has been developed to characterize the size dependent levels of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) contained in fly ash particles from a municipal solid waste incinerator (MSWI). Gravitational SPLITT fractionation (GSF), a relatively new technique for the fast and continuous separation of micron sized particles, was used to fractionate a fly ash sample, directly collected from a bag-filter house of MSWI in Korea, into six different size groups (<1.0, 1.0-2.5, 2.5-5.0, 5.0-10, 10-20, and 20-53 microm in diameter) in water solution, and the resulting fractions are examined by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) in order to determine the concentration of PCDD/Fs according to these particle sizes. The results from SPLITT fractionation show that approximately 54% of the fly ash particles (sieved fraction <53 microm) by weight have been found to be smaller than 5.0 microm excluding the water soluble matter in the sample. From the HRGC/HRMS measurements, particle fractions in the size range of PM 1.0-2.5 and 2.5-5.0 appear to carry about 76 and 79 ng/g of PCDD/Fs which are relatively larger than those found in other diameter ranges. Principal component analysis (PCA) shows that particles larger than 5.0 microm are clustered into a group predominantly containing low chlorinated dioxins and fractions smaller than 5.0 microm into another group with lower chlorinated furans. This study demonstrated that the combining GSF with a secondary analytical method such as HRGC/HRMS has the potential to obtain size dependent information of particulate materials in relation to their production processes, chemical compositions, environmental fates, and other factors.

Determination of drugs in surface water and wastewater samples by liquid chromatography–mass spectrometry: methods and preliminary results including toxicity studies with Vibrio fischeri

In the present work a combined analytical method involving toxicity and liquid chromatography–electrospray ionization-mass spectrometry (LC–ESI-MS) was developed for the determination of pharmaceutical compounds in water samples. The drugs investigated were the analgesics: ibuprofen, ketoprofen, naproxen, and diclofenac, the decomposition product of the acetyl salicylic acid: salicylic acid and one lipid lowering agent, gemfibrozil. The selected compounds are acidic substances, very polar and all of them are analgesic compounds that can be purchased without medical prescription. The developed protocol consisted, first of all, on the use Microtox ® and ToxAlert ®100 toxicity tests with Vibrio fischeri for the different pharmaceutical drugs. The 50% effective concentration (EC 50) values and the toxicity units (TU) were determined for every compound using both systems. Sample enrichment of water samples was achieved by solid-phase extraction procedure (SPE), using the Merck LiChrolut ® EN cartridges followed by LC–ESI-MS. Average recoveries loading 1 l of samples with pH=2 varied from 69 to 91% and the detection limits in the range of 15–56 ng/l. The developed method was applied to real samples from wastewater and surface-river waters of Catalonia (north-east of Spain). One batch of samples was analyzed in parallel also by High Resolution Gas Chromatography coupled with Mass Spectrometry (HRGC–MS) and the results have been compared with the LC–ESI-MS method developed in this work.

Design of a separation-free airfoil with outer-flow suction over a certain range of angles of attack

The problem of the design of an airfoil with slot air suction from the outer flow for a prescribed velocity distribution over the airfoil contour that ensures the absence of flow separation over a given range of angles of attack is formulated and solved. The proposed combined numerical and analytical method of airfoil design within the framework of the inviscid incompressible fluid model is based on the theory of inverse problems of aerohydrodynamics. Separationless flow past the airfoil is achieved by eliminating the falling velocity intervals from the specified velocity distribution in two given flow regimes. The flow past an airfoil with outer-flow suction is determined not only by the angle of attack as for an impermeable airfoil but also by the value of the suction mass flow. The slot is modeled by an annular channel with constant velocities on the walls. To satisfy the problem solvability conditions, free parameters are introduced into the initial velocity distribution. Examples of airfoil design are given.

A combined analytical singularity subtraction method and compact implicit differencing scheme for aerodynamic mixing

In spite of the rapid advances in both scalar and parallel computational tools, the large number and breadth of variables involved in both design and inverse problems make the use of sophisticated fluid flow models impractical. With this restriction, it may be concluded that an important family of methods for mathematical/computational development are reduced or approximate models. In this study, a combined perturbation/numerical modeling methodology is developed. The numerical portion of the model uses a compact finite difference scheme, while analytical solutions are used to resolve singular behavior that is inherent to this flow. Solutions are presented to illustrate the efficiency of this methodology.

A methodology for the determination of dynamic instabilities in a car disc brake

The dynamics of a car disc brake system is investigated by a combined analytical and numerical method. The disc is rotated past the stationary pads and calliper in sliding friction at constant speed. The modal data of the disc are obtained by means of modal testing whereby a dynamic model for the disc is derived based on the thin plate theory. Then the pads, calliper and mounting are analysed by means of the finite element method. Finally the equations of motion for the whole disc brake system are established through the interfaces between the pads and the disc. The stability of the vibrating system is studied by the method of state space.

Bismuth cubic superconductors: polaronic and superconducting properties of the Rice–Sneddon model

The Rice–Sneddon model of cubic bismuth superconductors is studied by combined analytical, variational, and numerical methods. A new representation is introduced for the phononic degrees of freedom, which makes phonon wavefunctions at different sites to be orthogonal. Due to that, then, the generalized Lang–Firsov transformation with two variational parameters may be exactly performed. One parameter is the classical displacement, whereas the second one is the squeezing variable. The transformed, effective electronic Hamiltonian has the form of the extended Hubbard model with longer-range electron–electron interactions and negative value of the Hubbard interaction, U. This effective Hamiltonian is further studied by means of numerical and analytical methods. First, using the Lanczos diagonalization scheme, the polaronic properties of the derived model have been studied. Second, the superconducting transition temperature T c has been evaluated in the Hartree–Fock approximation. From the calculated values of T c it is argued that the bare, electronic interaction U should be close to+0.36 eV.

Dynamic analysis of framed structures with statistical uncertainties

The forced harmonic vibration analysis of portal frames consisting of viscously damped beams with spatial stochastic variation of mass and stiffness properties is considered. The analysis is based on the assembly of element stochastic dynamic stiffness matrices. The solution involves inversion of the global dynamic stiffness matrix, which, in this case, turns out to be a complex-valued symmetric random matrix. Three alternative approximate procedures, namely, random eigenfunction expansion method, complex Neumann expansion method and combined analytical and simulation method are used to invert the matrix. The performance of these approximate procedures is evaluated using Monte Carlo simulation results. Copyright © 1999 John Wiley & Sons, Ltd.

Heat Transfer in the Rod Bundles and Thermal Analysis of Constor RBMK Cask Under Normal Storage Conditions

For demonstrating the safety of the casks intended for spent nuclear fuel transport and storage, the maximum temperature of the nuclear fuel rod cladding must be defined. For the gas filled CONSTOR RBMK metal-concrete cask developed jointly by GNB (Germany) and AOOT NPO CKTI (Russia) for RBMK-1000/1500 assemblies (Russian design) storage and transport the thermal analysis has been carried out for normal and fire accident conditions of operation. This paper is devoted to the description of the method applied to the analysis of heat transfer in the basket with assemblies disposed in the cask cavity. The combined analytical and numerical method for heat transfer calculation in the cask cavity based on a two-zone model of heat transfer inside the assembly has been developed and verified by means of the tests performed with an electrically heated bundle model consisting of 127 rods. One of the main features of the method is the real multi-rod assembly substitution by a homogenous heat-releasing bar with effective heat conductivity enclosed in the heat-conducting casing which models the basket tube.

Optimum Conditions for Composites Fiber Coating by Chemical Vapor Infiltration

A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration. For a first‐order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specific surface area, effective diffusivity or preform thickness, nor on the gas‐phase yield of the deposition reaction. Further, this optimum pressure is unaltered by the additional constraint of a prescribed deposition uniformity. Optimum temperatures are obtained using an analytical expression for the optimum value along with numerical solutions to the governing transport equations. These solutions account for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Sample calculations are presented for coating preform fibers with boron nitride.

Semi-analytical finite element analysis of a strip footing on an elastic reinforced soil

A plane strain elastic interaction analysis of a strip footing resting on a reinforced soil bed has been made by using a combined analytical and finite element method (FEM). In this approach the stiffness matrix for the footing has been obtained using the FEM. For the reinforced soil bed (halfplane) the stiffness matrix has been obtained using an analytical solution. For the latter, the reinforced zone has been idealised as (i) an equivalent orthotropic infinite strip (composite approach) and (ii) a multilayered system (discrete approach). In the analysis, the interface between the strip footing and reinforced halfplane has been assumed as (i) frictionless and (ii) fully bonded. The contact pressure distribution and the settlement reduction have been given for different depths of footing and scheme of reinforcement in soil. The load–deformation behaviour of the reinforced soil obtained using the above modelling has been compared with some available analytical and model test results. The equivalent orthotropic approach proposed in this paper is easy to program and is shown to predict the reinforcing effects reasonably well.