Electrochemical reduction of camphorquinone in DMF in the presence of a proton donor

The electroreduction of camphorquinone in DMF, at mercury electrodes, was investigated by a variety of techniques. In DMF, in the absence of proton donor, camphorquinone exhibits two one-electron waves: the first, a one-electron reversible wave to be due to a reversible charge transfer without a coupled chemical reaction. After the first charge transfer, the semidione anion radical is reduced to the dianion. The irreversibility of the second wave derives from a fast irreversible protonation of the dianion. A wide variety of changes in behaviour is observed in the reduction of camphorquinone as increasing amounts of benzoic acid are added: a new two-electron irreversible wave appears at a potential less negative than the original wave. A proton donor to substrate ratio of 2 is required to completely suppress the two original waves. A mechanism for the electroreduction of camphorquinone is proposed and discussed on the basis that the prewave current is controlled by the diffusion of the undissociated acid species and that the undissociated acid, rather than the solvated proton, takes part in the protonation, prior to the charge transfer.     

Determination of nitrate with a flow-injection system combining square-wave polarographic detection with on-line deaeration

The combination of a flow-injection system with square-wave polarography and on-line deaeration is applied to the determination of nitrate, utilizing the catalytic reaction between nitrate and uranyl ion. The method is simple, rapid (60 samples h^?1), sensitive and accurate, with a detection limit of 2 μM nitrate. The method has been applied to the determination of nitrate in drinking and river waters.     

Hand-held lead analyzer

The design and operation of a hand-held electrochemical analyzer for field screening of trace lead are described. The stripping-based instrument meets the size, weight and power-consumption requirements of many decentralized lead testings, while maintaining the high sensitivity and reliability of centralized stripping operations. When coupled to screen-printed disposable sensors, the unit's response varies linearly with the lead level between 20 and 300 mug/l (50-s deposition). Comparison with lead results obtained with the small and established instruments yielded an excellent correlation (r=0.999). Convenient quantification of lead in drinking water is accomplished with quiescent, nondeaerated small samples. Such performance and portability hold great promise to a host of environmental, clinical, or industrial applications.     

Attempted synthesis of a substituted [2.2.2]propellane derivative from triptycene derivatives

Bromotriptycene derivatives substituted at the bridgehead were subjected to varying reaction conditions in the attempt to obtain a substituted [2.2.2]propellane. The desired cyclization was not effected. The bromine atoms were replaced by hydrogens.     

Gel permeation chromatography of simple anions in aqueous solutions

Semi-automatic liquid chromatographic apparatus is described for the separation of simple inorganic anions in aqueous solution, using dextran gels for the separation and differential conductivity for detection. The influence of different types of eluent on the degree and order of separation is discussed.     

A flow detector based on square-wave polarography at the dropping mercury electrode

Square-wave polarography (s.w.p.) at the DME has been adapted for detection in various analytical flow systems. The combination of high sensitivity with rapid potential scan rates results in detector characteristics significantly superior to those previously reported for techniques involving constant applied potential. In an automated flow system for the analysis of discrete samples, s.w.p. allows sensitive and reproducible multi-component sample analysis, at a sampling rate of 22.5 samples per hour (at a 1:1 sample/wash ratio and with relatively low sample volumes). The electrochemical selectivity of the detector may be exploited for monitoring Chromatographic column effluents, in cases where the chromatographic separation is incomplete: species eluted simultaneously but having different reduction potentials can be determined with satisfactory sensitivity. The in-situ monitoring system based on s.w.p. allows rapid simultaneous determinations (~ 300 per hour) of a number of contaminants present at the sub-ppm level; because of its long-term stability and reproducibility, it seems well suited for continuous contaminant control.     

Nonlinear Dynamics and Stability of a Machine Tool Traveling Joint

In this work, we investigate the nonlinear dynamics and stability of a machine tool traveling joint. The dynamical system considered includes contacting elements of a lathe joint and the cutting process where the onset of instability is governed by mode coupling. The equilibrium equations of the dynamical system yield a unique fixed point that can change its stability via a Hopf bifurcation. The unstable domain is primarily governed by the cutting tool location, the contact stiffness of the joint and the depth of material to be removed. Self excited vibrations due to a mode coupling instability evolve around the unstable fixed point and one or more limit cycles may coexist in the statically unstable domain. Stability and accuracy of the approximate analytical solutions are analyzed by applying Floquet analysis. Perturbation of the dynamical system with weak periodic excitation results with periodic and aperiodic solutions.