Determination of Chlorinity of Water without the Use of Chromate Indicator

A new method for determining chlorinity of water was developed in order to improve the old method by alleviating the environmental problems associated with the toxic chromate. The method utilizes a mediator, a weak acid that can form an insoluble salt with the titrant. The mediator triggers a sudden change in pH at an equivalence point in a titration. Thus, the equivalence point can be determined either potentiometrically (using a pH meter) or simply with an acid-base indicator. Three nontoxic mediators (phosphate, EDTA, and sulfite) were tested, and optimal conditions for the sharpest pH changes were sought. A combination of phosphate (a mediator) and phenolphthalein (an indicator) was found to be the most successful. The choices of the initial pH and the concentration of the mediator are critical in this approach. The optimum concentration of the mediator is ca. 1~2 mM, and the optimum value of the initial pH is ca. 9 for phosphate/phenolphthalein system. The method was applied to a sample of sea water, and the results are compared with those from the conventional Mohr-Knudsen method. The new method yielded chlorinity of a sample of sea water of (17.58 ± 0.22) g/kg, which is about 2.5% higher than the value (17.12 ± 0.22) g/kg from the old method

Advances in Derivative Voltammetry - A Search for Diagnostic Criteria of Several Electrochemical Reaction Mechanisms

New methods for analysis of current-potential curves in terms of their derivatives are presented for studying various types of electrode processes – such as simple electron transfer reactions (reversible, quasi-reversible, and irreversible electron transfer) as well as chemically coupled electron transfer reactions along with a diagnostic scheme for differentiating these various types of electrochemical reaction mechanisms. Expressions for first- and higher order derivatives are derived from theoretical analytical solutions for currents for the different types of electrode mechanisms. The derivative curves are analyzed in terms of various parameters which characterize peak shape or peak symmetry with an emphasis on the second derivatives with well-defined anodic and cathodic peaks. Second derivatives can yield, in a simpler manner, the symmetry ratios; i.e., a ratio of anodic to cathodic peak-currents (ipa/ipc), and a ratio of anodic to cathodic peak-widths (Wpa/wpc) and a ratio of anodic to cathodic peak potential differences (ΔEpa/ΔEpc) or a peak separation (Epa-Epc) are evaluated, and these ratio can be related to kinetic parameters associated with a particular types of electrode mechanisms. Peaks are found to be symmetrical for a simple reversible electron transfer process (Er). However, peaks become asymmetrical when the electron transfer become slower (namely, irreversible, Eirr) or e− transfer reaction is coupled with homogeneous chemical reactions such as a prior reaction (CEr) or a follower-up reaction (ECr). From measured values of such symmetry ratios above, one can gain insight to the nature of the electrochemical systems enabling us to determine various kinetic parameters associated with a system. A diagnostic criteria for assigning an electrode mechanism is devised based on the values of asymmetry parameters measured, which are unity for a simple reversible electron transfer process

Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration

We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov, Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.open1

Evaluation of the Function Exp (X2) Erfc (X) to Higher Precisions for Higher-Order Derivative Polarography of CE-Type Electrode Process

The function exp(x2)erfc(x), which is often encountered in studies of electrode kinetics, is evaluated to an extended precision with 32 significant decimal digits in order to find theoretical relationships used in derivative polarography/voltammetry for a chemically-coupled electrode process. Computations with a lower precision are not successful. Evaluation of the function is accomplished by using three types of expansions for the function. Best ranges of arguments are selected for each equation for particular precisions for efficiencies. The method is successfully applied to calculate higher-order derivatives of the current-potential curves in all potential ranges for a reversible electron transfer reaction coupled with a prior chemical equilibrium (i.e., a CE type process). Various parameters that characterize the peak asymmetry (such as ratios of peak-heights, ratios of half-peak-widths, and separations in peak-potentials) are analyzed to find how kinetic and thermodynamic parameters influence shapes of the derivatives. The results from the CE process is compared with those from an EC process in which a reversible electron transfer is coupled with a follow-up homogeneous chemical reaction. The two processes exibit quite contrasting differences for values of the parameters

The efficacy of preoperative PET/CT for prediction of curability in surgery for locally advanced gastric carcinoma

<p>Abstract</p> <p>Background</p> <p>The benefits of preoperative ¹⁸FDG-PET/CT for gastric cancer remain uncertain. The aim of this study was to investigate the effects of preoperative ¹⁸FDG-PET/CT on the surgical strategy for locally advanced gastric cancer retrospectively.</p> <p>Methods</p> <p>From January 2007 to November 2008, ¹⁸FDG-PET/CT was performed in 142 patients who had been diagnosed with advanced gastric cancer by computed tomography or gastrofiberscope findings.</p> <p>Results</p> <p>Detection rates were 88.7% (126/142) for primary tumors and 24.6% (35/142) for local lymph nodes (LN). Nine patients with metastatic lesions underwent induction chemotherapy without operation. Of 133 patients subjected to operation, positive FDG uptake in primary tumors (<it>p </it>= 0.047) and local lymph nodes (<it>p </it>< 0.001) was related to non-curable operations. The mean standard uptake value (SUV) of primary tumors of patients who underwent non-curable operations was significantly higher than that of patients with curable operations (<it>p </it>= 0.001). When the SUV was greater than 5 and FDG uptake of LN was positive, non-curable operations were predicted with a sensitivity of 35.2%, a specificity of 91.0% and an accuracy of 76.7%.</p> <p>Conclusions</p> <p>High SUV of the primary tumor and positive FDG uptake in local lymph nodes at PET/CT could predict non-curative resection in locally advanced gastric cancer. Therefore, information from preoperative PET/CT can help physician decisions regarding other modalities without laparotomy.</p