Performance of synthetic storm technique in estimating fade dynamics in equatorial Malaysia

In this paper, the synthetic storm technique (SST) is applied to 1‐minute rainfall rate collected from a rain gauge to predict the fade dynamics of the signal in an earth‐to‐satellite link in an equatorial climate location without the needs of satellite beacon measurements. The obtained results are compared with the statistics calculated from measured rain attenuation and with the ITU recommendation model. As for fade duration, a good agreement with measurements has been found together with a significant improvement in terms of prediction errors with respect to the ITU‐R model. Synthetic storm technique is also able to predict fade slope statistics fairly well and has equivalent performance of ITU‐R model.     

Three-way Resolution of the Overlapping Ultrahigh-performance Liquid Spectrochromatograms for the Analysis of a Quaternary Mixture Using Parallel Factor Analysis

This paper presents a new application of three-way parallel factor analysis (3W-PARAFAC) model to the coeluting spectrochromatograms for the quantitative resolution of a quaternary mixture system consisting of paracetamol, propyphenazone, and caffeine with aspirin as an internal standard. Spectrochromatograms of calibration standards, validation sets, and unknown samples were recorded as a function of retention time and wavelength in the range of 0.0–2.5?min and 200–400?nm, respectively, using ultra-performance liquid chromatography with photodiode array detection (UPLC-PDA). Three-way UPLC-PDA data array X (retention time?×?wavelength?×?sample) was obtained from the data matrices of the spectrochromatograms. 3W-PARAFAC decomposition of three-way UPLC-PDA data array provided three loading matrices corresponding to chromatographic mode, spectral mode, and relative concentration mode. Quantitative estimation of paracetamol, propyphenazone, and caffeine in analyzed samples was accomplished using the relative concentration mode obtained by the deconvolution of the UPLC-PDA data set. The validity and ability of 3W-PARAFAC model were checked by analyzing independent test samples. It was observed from analyses that 3W-PARAFAC method has potential to uniquely resolve strongly overlapping peaks of analyzed compounds in a spectrochromatogram, which was obtained under experimental conditions consisting of the lower flow rate, short run time, and simple mobile phase composition. The proposed three-way chemometric approach was successfully applied to the simultaneous quantification of paracetamol, propyphenazone, and caffeine in tablets. Experiments showed that the determination results were in good agreement with label amount in commercial pharmaceutical preparation.     

Application of Multivariate Calibration Techniques to HPLC Data for Quantitative Analysis of a Binary Mixture of Hydrochlorathiazide and Losartan in Tablets

New multivariate approaches have been applied to high-performance liquid chromatography (HPLC) with multiwavelength photodiode-array (PDA) detection. Multivariate calibration techniques such as partial least squares (PLS), principal component regression (PCR), classical least squares (CLS), and inverse least squares (ILS) was subjected to HPLC data for simultaneous quantitative analysis of synthetic binary mixtures and a commercial tablet formulation containing hydrochlorothiazide (HCT) and losartan potassium (LST). The combined use of HPLC and multivariate calibrations has been denoted HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS. Successful chromatographic separation of the two active compounds and enalapril maleate, used as internal standard (IS), was accomplished by means of a 4.6 mm i.d. × 250 mm, 5 m particle, Waters Symmetry C₁₈ reversed-phase column and a mobile phase consisting of 60:40 acetate buffer (0.2 M, pH 4.8)–acetonitrile (v/v, 60:40). HPLC data based on the ratio of analyte peak areas to IS peak area were obtained by PDA detection at five-wavelengths (250, 255, 260, 265, and 270 nm). The HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS calibration plots for hydrochlorothiazide and losartan potassium were constructed separately by using the peak-area ratios corresponding to the concentrations of each active compound. The HPLC multivariate calibrations obtained were tested for different synthetic mixtures containing HCT and LST in the presence of the IS. These multivariate chromatographic methods were also applied to a commercial pharmaceutical dosage form containing HCT and LST. The results obtained from the multivariate calibrations were compared with those obtained by use of another, classical HPLC method using single-wavelength detection.Revised: 29 September 2004 and 4 January 2005     

Oxidation of l-methionine with aqueous chromic acid: a kinetic study

The kinetics of oxidation of l-methionine by chromic acid in acidic medium (pH=0.83–2.2) has been studied spectrophotometrically. The effect of l-methionine and chromium(VI) concentrations on the rate of the reaction was determined. The reaction rate decreases with increasing the pH of the medium. The kinetics of the formation of a chromium(III) complex conform to the rate law:with k1=7.5×10–2s–1 and Kes1=43.85 at constant [H+]=1.9×10–2moldm–3 and [l-methionine]T= 2.0×10–2moldm–3. The same values were found with [l-methionine]T variation at constant [H+]. The reaction proceeds through formation of chromium(VI)-l-methionine ester in a rapid pre-equilibrium step, followed by a slower redox reaction of the ester. The present study provides kinetic evidence for formation of a complex ion (ester). One mole of Cr2O72– oxidizes four moles of l-methionine, which acts as a monodentate ligand and binds to chromium(VI) through the sulfur atom. The coordinated sulfur atom of l-methionine–chromium(VI) ester is responsible for the oxidative degradation (breaking of the C1-C2 bond) of l-methionine. Coordinated oxygen of the carboxylate group inhibits the cleavage of the C1-C2 bond.     

Studies on the pitting corrosion of zinc in aqueous solutions II. Measurement of pitting corrosion currents operating under natural conditions

A simple experimental arrangement was applied for the measurement and the evaluation of pitting corrosion currents operating under natural conditions. The feasibility of the procedure was examined by using Zn as a test metal, K₂CrO₄, Na₂HPO₄ and Na₂WO₄ as inhibitors, and Cl^?, Br^? and I^? as pitting corrosion agents. Both the type and concentration of the inhibiting and corroding agents were varied in a programmed manner. In CrO₄^2? and HPO₄^2? solutions, the pitting corrosion currents started to flow after an induction period, which decreased with increase in the concentration of the attacking agent. In WO₄^2? solutions, on the other hand, initially high currents were recorded due to the reduction of the agent to soluble, non-inhibiting species.In all solutions tested the corrosion current reached steady-state values which depended on the type and concentration of both the inhibiting and the aggressive anions. When keeping the inhibitor concentration constant, the corrosion current varied with the concentration of the aggressor according to: log i_corr = a₁ + b₁ log c_agg On the other hand, in solutions of constant aggressor concentration, with varying inhibitor amounts, the relation was: log i_corr = a₂ ? b₂ log c_inh where a₁(a₂) and b₁(b₂) are constants.The two equations were derived theoretically on the basis of competitive adsorption of the two counteracting agents on the surface of the metal. Comparison between the experimental values of a and b, with the corresponding terms of the theoretical equations was made.The aggressivity of the three tested anions decreases in the order Cl^? > Br^? > I^?, whilst inhibition varied as CrO₄^2? > HPO₄^2? > WO₄^2?.     

A new enzyme electrode based on ascorbate oxidase immobilized in gelatin for specific determination of l-ascorbic acid

A biosensor for the specific determination of l-ascorbic acid in fruit juices and vitamin C tablets was developed using ascorbate oxidase (EC 1.10.3.3) from cucumber (Cucumis sativus L.) in combination with a dissolved oxygen probe. Ascorbate oxidase immobilized with gelatin using glutaraldehyde and fixed on pretreated teflon membrane served as an enzyme electrode. The phosphate buffer (50 mM, pH 7.5) and 35 degrees C were established as providing the optimum conditions. The biosensor response depends linearly on l-ascorbic acid concentration between 5.0x10(-5) and 1.2x10(-3) M with a response time 45 s. The biosensor is stable for more than 2 months, while more than 200 assays were performed. The results obtained for fruit juices and tablets were compared with DCIP (2,6 dichlorophenolindophenol) method.     

Derivatives of substituted 3‐trichlorogermylpropionic acid

The central Ge atoms in the structures of 3‐(2‐fluoro­phenyl)‐3‐(tri­phenyl­germyl)­propionic acid, [Ge(C₆H₅)₃(C₉H₈FO₂)], 3‐(2‐tolyl)‐3‐(tri‐4‐tolyl­germyl)­propionic acid, [Ge(C₇H₇)₃(C₁₀H₁₁O₂)], and 3‐(4‐tolyl)‐3‐(tri­benzyl­germyl)­propionic acid, [Ge(C₇H₇)₃(C₁₀H₁₁O₂)], are four‐coordinate with slightly distorted tetrahedral geometry. The Ge—Csp³ distances [1.970 (3)–1.997 (3) Å] are significantly longer than the Ge—C_aromatic distances [1.940 (3)–1.959 (2) Å]. In all three structures, the mol­ecules form dimeric pairs about inversion centres through strong hydrogen‐bonding interactions between carboxyl­ic acid groups.     

Zum Mechanismus der Ninhydrin-Reduktion nach polarographischen Untersuchungen in methanolischen Lösungen

Zusammenfassung Ergebnisse der polarographischen Reduktion von Ninhydrin in wasserfr. methanol. Lösungen werden mitgeteilt. Der Einfluß von Protonendonatoren (z. B. Benzoesäure) sowie von Substanzen, welche Protonisierungsreaktionen und die Wasserstoffabscheidung katalysieren (z. B. N,N-Dimethyl-p-phenylendiamin=DMPD) wird ermittelt. Unter bestimmten Bedingungen wird auch die dritte, soloatisierte Ketogruppe reduzierbar. Die Desoloatation wird auf die stufenweise Abdissoziation von H⁺ und OH^– bzw. OR^– zurückgeführt.Das an der Elektrodenoberfläche adsorbierteDMPD wirkt bei der Reduktion der freien Ketogruppen als Protonenüberträger, bei der Reduktion der soloatisierten aber auch als Protonenakzeptor.Die exper. Ergebnisse der polarographischen Reduktion in methanol. Lösung stützen den aus vorangegangenen Untersuchungen in wäßr. Lösung aufgestellten Reduktionsmechanismus.

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The polarographic behaviour of ninhydrin is investigated in water-free methanolic solutions. The effect of addition of protondonors (e.g., benzoic acid) and of substances catalyzing protontransfer-and hydrogen-discharge-reactions (e.g., N,N-dimethyl-p-phenylenediamine=DMPD) on the characteristics of the polarographic waves is described. Under well defined conditions all three keto-groups can be reduced. The reduction of the soloated keto-group involves the elimination of water by stepwise dissociation of H⁺ and OH^– (OR^–) ions. DMPD, adsorbed on the surface of the electrode, acts as proton-carrier in the reduction of the two free keto-groups, and also as proton-acceptor in the reduction of the third, soloated group.The experimental results of the polarographic reduction of ninhydrin in methanol confirm the mechanism of reduction in aqueous solutions previously presented.

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Mit 2 Abbildungen     

Polarographic Determination of Famotidine through Complexation with Nickel(II) Chloride

The present investigation describes the development of a sensitive, rapid polarographic method for the determination of famotidine in pure form and in certain dosage forms. The proposed method depends upon studying the polarographic activity of Nickel(II)‐famotidine complex in Britton Robinson buffer over the pH range 4–8 and its usefulness in the analysis of famotidine using direct current (DC_t), differential pulse (DPP), and alternating current (AC_t) polarography. The different experimental parameters affecting the cathodic waves were carefully investigated and optimized. Moreover, to check the validity of the proposed method, the standard addition method was applied by adding famotidine to the previously analyzed tablets. The recovery of the drug was calculated by comparing the concentration obtained from the spiked mixtures with those of the pure drug. The results of analysis of commercial tablets and the recovery study suggested that there is no interference from any excipients, which are present in tablets. Statistical comparison of the results was performed with regard to accuracy and precision using student's t‐test and F‐ratio at 95% confidence level. There is no significant difference between the comparison and proposed method with regard to accuracy and precision.     

Filippov–Pliss lemma and m-dissipative differential inclusions

In the paper we prove a variant of the well known Filippov–Pliss lemma for evolution inclusions given by multivalued perturbations of m-dissipative differential equations in Banach spaces with uniformly convex dual. The perturbations are assumed to be almost upper hemicontinuous with convex weakly compact values and to satisfy one-sided Peron condition. The result is then applied to prove the connectedness of the solution set of evolution inclusions without compactness and afterward the existence of attractor of autonomous evolution inclusion when the perturbations are one-sided Lipschitz with negative constant.