Inductively-coupled plasma-optical emission spectrometry Application to the determination of molybdenum, cobalt and boron in soil extracts

An inductively-coupled radiofrequency plasma method applicable to the determination of Mo, Co and B in soil extracts has been developed. The interferences caused by some common metals and acids have been investigated. The detection limits observed at the chosen wavelengths were 0.01, 0.05 and 0.05 ppm for Mo, Co and B respectively. The mean relative standard deviation determined over an extended period of time was 0.9%.     

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

Determination of copper(II) based on its catalytic effect on thiosemicarbazide-H(2)O(2)-CTMAB chemiluminescence reaction

A novel chemiluminescence (CL) reaction, thiosemicarbazide (TSC)–H₂O₂, for the determination of copper at nanogram per milliliter level in batch type is described. The method is based on the catalytic effect of copper(II) on the oxidation of TSC with hydrogen peroxide to produce light emission. The emitted light was observed by using a conventional fluorescence detector. In the optimum conditions, calibration graph was linear in the range of 0.1–1.3 ppm. The limit of detection was 10 ppb. The relative standard deviation for five determinations of 0.5 ppm copper(II) was 1.93%. The proposed method permitted the selective and sensitive determination of Cu(II) in human hair and wheat flour with sufficient precision. The possible mechanism for the new chemiluminescence reaction was also discussed.     

Reverse micelle coacervate-based extraction combined with electrothermal atomic absorption spectrometry for the determination of arsenic in water and oyster tissue samples

A tyrosinase-based biosensor was constructed by immobilizing the enzyme on diazonium-functionalized screen-printed gold electrodes. Under optimized conditions, the biosensor exhibited rapid response to the changes in the concentration of all the tested phenolic compounds (catechol, catechin, caffeic acid and gallic acid). Sensitivity, linear range and limit of detection (LOD) were determined, and catechol was found to display the highest sensitivity (36.3 mA?M^?1) and the lowest LOD (0.1 μmol?L^?1). The biosensor was successfully applied to the detection of polyphenols in tea samples.     

Cloud Point Preconcentration and Flame Atomic Absorption Spectrometric Determination of Cobalt and Nickel in Water Samples

 Cloud point methodology was successfully used to preconcentrate trace amounts of Co and Ni as a prior step to their determination by flame atomic absorption spectrometry. 1-Nitroso-2-naphthol and polyethylene glycol-p-nonylphenylether (PONPE 7.5) are used as hydrophobic ligand and nonionic surfactant, respectively. Optimization was performed of the variables effecting complexation and phase separation. Additionally, the influence of viscosity on the analytical signal was investigated. Under the experimental conditions used, preconcentration of only 10 mL of sample in the presence of 0.075% (v/v) PONPE 7.5 permitted the detection of 1.09 μg L⁻¹ of Ni and 1.22 μg L⁻¹ of Co with enhancement factors of 29 and 27 for Ni and Co, respectively. The relative standard deviations (n=5) at concentrations of 80 and 50 μg L⁻¹ for Co and Ni were 2.53 and 2.89%, respectively. Good recoveries in the range of 96–105% were obtained for spiked samples. The effect of different interferent species was studied. The proposed method was applied to the determination of Ni and Co in different water samples. Correspondence: Department of Analytical Chemistry, Faculty of Chemistry, Tabriz University, Tabriz, Iran. e-mail: manzoori@tabrizu.ac.ir Received September 1, 2002; accepted November 8, 2002     

A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.