A comparison of two test methods for determining elastomer physical properties

Accurate values of Poisson's ratio for elastomers are necessary, for example, in the stress analysis of rubber components. Poisson's ratio may be expressed in terms of the elastic and bulk moduli of the elastomer. It is shown that errors in Poisson's ratio are small even though errors in experimental values of these moduli can be large.Two methods of measuring the moduli of elastiomers are described. Samples of nominally the same compounding formulation were tested by both methods and the results compared. Sources of error are discussed and comments made regarding the handling of the two experimental facilities.     

Electrochemical nitric oxide sensor preparation: a comparison of two electrochemical methods of electrode surface modification

Platinum electrodes modified with Mn(II) 5-(N-(8-pyrrole-yl-3,6-dioxa-1-aminooctane)phenylamide-10,15,20-trimethoxyphenylporphyrin (Mn(II)triOMeTCPPyP) using multi-sweep cyclic voltammetry and differential pulse amperometry were evaluated as electrocatalytic surfaces for the oxidation of nitric oxide. The electrodes modified using the pulse amperometric approach were more sensitive towards the detection of nitric oxide. The increased sensitivity led to the attainment of a wider linear dynamic range for the quantification of nitric oxide.     

Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles

Formation of thiophene-substituted isoxazoles by reaction of chalcone dibromides and 1,3-diketones with hydroxylamine hydrochloride has been examined under different conditions. Use of KOH as base in the reaction of dibromide chalcone analogs with hydroxylamine hydrochloride yields mixtures of isomeric isoxazoles in modest yields. Replacement of KOH with pyridine affords negligible amounts of isoxazoles only, the intermediate 2-bromoprop-2-en-1-one being isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride, irrespective of reaction pH. At low pH, regioselectivity was poorer than that observed for reaction of chalcone dibromides with hydroxylamine hydrochloride, but yields were substantially better. At high pH, yields were comparable with those at low pH and regioselectivity for 3-aryl-5-(2-thiophenyl)isoxazole was slightly enhanced, but the dioxime corresponding to the initial 1,3-diketone was also produced in low yields as a mixture of stereoisomers.     

A comparison of two rapid methods for the analysis of copper smelting slags by atomic absorption spectrometry

A fusion method with anhydrous lithium metaborate is compared with a hydrofluoric acid decomposition method for the analysis of copper smelting slags. Atomic-absorption spectrometry is used to determine silica, alumina, copper, zinc and iron in the resulting sample solutions. The accuracy and precision of both methods are found to be similar. The fusion method is more convenient for general routine use.     

ML or NJ-MCL? A comparison between two robust phylogenetic methods

Large-scale gene sequencing gives an opportunity to reconstruct the tree of life and histories of multigene species phylogenies from very large datasets. A primary need for reconstructing large-scale phylogenies is a computationally efficient and accurate method. Current efforts to achieve such a goal include NJ-MCL² described by Tamura et al. (2004; 2007), an algorithm based on maximum likelihood (ML) and neighbor joining (NJ) algorithms. Although it has been reported that the NJ-MCL method performs better than the NJ method, studies comparing the accuracy of the ML and NJ-MCL methods are lacking. Here, accuracy of the NJ-MCL and the ML methods are examined. The concatenation approach (by progressive addition of genes) is used in a biologically realistic computer simulation to infer the accuracy of the methods. Simulation results clearly show that although NJ-MCL is computationally efficient and outperforms NJ method, the ML method is clearly much more accurate than the NJ-MCL method. The results encourage the use of the ML algorithm where datasets include up to several hundred species, but for reconstructing grand-scale phylogenies (i.e., where several thousand of taxa are included) NJ-MCL is preferred.     

NAA and ICP-MS: A comparison between two methods for trace and ultra-trace element analysis

NAA and ICP-MS are both highly sensitive methods for multi-element trace-and ultra-trace element determination. A comparison between analytical figures of merit of both methods is made. Both methods have specific advantages that put them beyond competition for certain applications. It is concluded that ICP-MS can replace NAA for many routine analyses. NAA remains essential as a highly reliable and accurate reference method.     

A comparison of three methods for cholinesterase analysis

Three methods of cholinesterase analysis in blood are compared: the ΔpH (modified Michel method), pH Stat, and radiometric methods. The ΔpH method was determined to be the best choice for routine laboratory screeening for organophosphate exposure. The methods all agree within experimental variation. The radiometric method uses a thin-layer chromatography (TLC) separation of acetate (¹⁴C) activity from acetylcholine (¹⁴C) activity with direct β counting or scintillation counting to determine the concentration of acetate activity. The methods were compared on freeze-dried human blood and on experimentally carbamate-inhibited mouse blood. The radiometric analysis may be performed using as little as 5 μl of blood. The radiometric method may enhance the ability to detect sublethal exposure to cholinesterase inhibitors. It should be of particular use where sampling size is of greatest importance.     

A comparison of geometric methods with other methods for the characterization of density matrices

Some recently developed geometric methods for characterizing the subset of density matrices within the space of Hermitian matrices are compared with methods commonly used for the approximate characterization of reduced density matrices. The decomposition of a density matrix into components in terms of the reducing basis set is compared with decomposition in terms of representations of U(r).     

A comparison of methods for the determination of platinum in ores

Fire-assay and wet-extraction methods of determining platinum in ores have been evaluated. The fire-assay procedure using lead as a collector was used in combination with flame and flameless atomic-absorption, emission spectroscopy and X-ray fluorescence. In this last method flattened silver beads were analysed directly, whereas for the other methods the beads were dissolved in aqua regia and the solutions made up with concentrated hydrochloric acid before analysis. The wet procedures involved treatment of the ores with acids and subsequent analysis by flame atomic-absorption or by spectrophotometry after treatment with tin(II) chloride. Chromatographic, ion-exchange and solvent-extraction procedures were used to isolate platinum from base metals, the other platinum metals and gold. Results for each ore by fire assay-flame atomic-absorption, fire assay-emission spectroscopy, and wet extraction combined with spectrophotometry, showed no difference at the 99% confidence level. X-Ray fluorescence and flameless atomic-absorption results tended to be high and low respectively. The most precise method was wet extraction followed by spectrophotometric determination. Emission spectroscopy and X-ray fluorescence generally yielded the poorest precision. Wet-extraction methods were time-consuming and since no advantage was gained in accuracy over the fire-assay methods, a combined fire assay-flame atomic-absorption system was the preferred method of analysis.     

Spectrofluorimetric determination of dipyridamole in serum--a comparison of two methods

Two spectrofluorimetric methods for the determination of dipyridamole in plasma are described. The thin-layer chromatographic-fluoridensitometric method utilizes 1 ml of plasma which is extracted at pH 10 with diethyl ether-dichloromethane (80:20). The organic phase is evaporated to dryness, reconstituted in 250 microliter dichloromethane and 5 microliter are spotted on a silica gel 60 plate. The plate is developed in ethyl acetate-methanol-ammonia (85:10:5), dried, dipped in a paraffin wax solution, dried, and scanned using 380 nm as excitation wavelength, a 430 nm cut-off filter, and collecting all emitted light on the photomultiplier. Quantitation was done by the external standard method, peak heights being measured and a calibration graph constructed. For the spectrofluorimetric method 1 ml of plasma is extracted at pH 10 with 8 ml of hexane-isoamyl alcohol (95:5) and the organic phase used directly for the measurement of the fluorescence intensity (excitation 405 nm, emission 495 nm). Quantitation was done by measuring the fluorescence of standards that were treated as above and constructing a calibration graph of concentration versus fluorescence intensity. Concentrations of unknowns were found by interpolation from this graph. The two methods were found to exhibit good correlation but the spectrofluorimetric method proved to be more amenable to the analysis of a large number of samples.     

A comparison of two methods for selecting vibrational configuration interaction spaces on a heptatomic system: ethylene oxide

Two recently developed methods for solving the molecular vibrational Schrodinger equation, namely, the parallel vibrational multiple window configuration interaction and the vibrational mean field configuration interaction, are presented and compared on the same potential energy surface of ethylene oxide, c-C(2)H(4)O. It is demonstrated on this heptatomic system with strong resonances that both approaches converge towards the same fundamental frequencies. This confirms their ability to tackle the vibrational problem of large molecules for which full configuration interaction calculations are not tractable.     

Determination of lead and cadmium in sediment slurries by ETA-AAS: A comparison of methods for the preparation and analysis of sediment slurries

Comparisons were made of various methods for the homogenization of sediment slurries for the determination of Pb and Cd by ETA-AAS. Homogenization techniques evaluated included the use of impact bead, propeller and foamless generators, vortexing and ultrasonic homogenization. On the basis of precision and accuracy, speed and ease of operation; the ultrasonic homogenization technique was clearly the method of choice. Precision obtained for this method using both reduced PdCl₂ modifier and the L'vov platform approaches what is obtained for aqueous solutions. Accuracy for Pb and Cd was excellent using both slurry and aqueous calibration standards with slurry standards being somewhat superior for Cd.     

A comparison of some integral methods

The integral methods proposed to compute the kinetic parameters of heterogeneous reactions under non-isothermal conditions are usually worked by the help of the least squares method and the obtained correlation coefficient is taken as a criterion to choose the best integral method.An analysis of several experimental data by mean of three different integral methods was performed by us and the results pointed out that this criterion, by itself, is not enough to provide reliable information on the kinetic parameters.It appears, thus, that the use of an integral method or another is a simple matter of researcher's choice.

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Zusammenfassung Integrationsmethoden zur Berechnung kinetischer Parameter von heterogenen Reaktionen unter nicht isothermen Bedingungen werden im allgemeinen nach der Methode der kleinsten Quadrate erarbeitet und der ermittelte Korrelationskoeffizient dient als ein Kriterium für die Auswahl der besten Integrationsmethode.Mittels drei verschiedenen Integrationsmethoden wurde eine Analyse verschiedener experimenteller Daten durchgeführt. Die Ergebnisse zeigen, daß dieses Kriterium allein nicht ausreicht, um ausreichende Informationen über die kinetischen Parameter zu liefern.Es scheint deshalb, daß die Verwendung der einen oder anderen Integrationsmethode einfach eine Wahl des Anwenders darstellt.

     

A general method for the preparation of N-monosubstituted-3-isothiazolamines

We describe here a novel and general high yield method for the synthesis of 3-alkyl and arylaminoisothiazoles, a previously unknown group of isothiazoles, by the reaction of ammonia with 3-halo-2-alkylisothiazolium salts. The mechanism of the reaction probably involves a ring opening followed by a recyclization to the title compounds.     

A review of sample preparation methods for the pesticide residue analysis in foods

The pesticide residues in foods have received increasing attention as one of the most important food safety issues. Therefore, more strict regulations on the maximum residue limits (MRLs) for pesticides in foods have been established in many countries and health organizations, based on the sensitive and reliable analysis methods of pesticide residues. However, the analysis of pesticide residues is a continuing challenge mainly because of the small quantities of analytes as well as the large amounts of interfering substances which can be co-extracted with them, often leading to experimental errors and damage to the analytical instruments. Thus, extensive sample preparation is often required for the pesticide residue analysis for the effective extraction of the analytes and removal of the interferences. This paper focuses on reviewing the recent development in the sample preparation methods for the pesticide residue analysis in foods since 2006. The methods include: liquid-liquid extraction (LLE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), gel permeation chromatography (GPC), solid-phase extraction (SPE), molecularly imprinted polymers (MIPs), matrix solid-phase dispersion (MSPD), solid-phase micro-extraction (SPME), QuEChERS, cloud point extraction (CPE) and liquid phase micro-extraction (LPME), etc. Particularly their advantages, disadvantages and future perspectives will be discussed.     

A comparison of the several methods for determination of specific IgE antibodies

The accuracy of measurement using kits in the clinical laboratories is important for the patient diagnosis and treatment. In the present paper, the AL-18, AlaSTAT, CAP, FAST and RAST methods were investigated and were compared among kits the results obtained with serum sample, for determination of specific IgE antibodies. Significant differences among kits were observed from the results of those methods. One of the reasons, why the data discrepancy exists, is that each kit uses a different reference and a different inclusion method of allergen. For the evaluation of data discrepancy among those kits, it might be important that the clinical history of symptoms and in vivo tests against the different allergens compared with results of in vivo tests.     

High yield selective 3′-silylation of ribonucleosides

Procedures have been developed which permit the highly selective silylation of the 3′-hydroxyl of ribonucleosides to produce 3′,5′-diprotected derivatives in high yields.     

New methods for the preparation of aryl 2-iminoimidazolidines

A divergent strategy for the synthesis of 1-aryl- and 2-aryl-2-iminoimidazolidines is presented. Cyclization of N-Boc-N′-aryl-N′′-(2-hydroxyethyl)guanidines in the presence of methanesulfonyl chloride and triethylamine or sodium hydride at 0 °C affords the corresponding 2-iminoimidazolidines in good yields.