Tsugio Kojima

An analog simulation of non-integer order transfer functions for analysis of electrode processes

Summary Diffusion processes both with and without chemical reactions in the solution can be expressed by non-integer order transfer functions for the concentration change at the electrode surface and the current density. The principle and the method of simulating these non-integer order transfer functions by RC-networks and operational amplifiers, using the graphical approximation on the Bode diagram, are shown and discussed. It is proved that the present method is quite useful not only for the simulation of a simple diffusion process but also for a basic model experiment of monolayer problems and even for computational measurements of the activity of a deposited metal in real systems.

Application of pseudo-random signals and cross-correlation techniques in electroanalytical chemistry

Summary The significance of application of white noise and cross-correlation function techniques in electroanalytical chemistry is described. The simplest pseudo-random signal generator and the correlator which avoid the use of large memory are constructed and applied to a few electrode systems. The responses obtained and their frequency profiles agree well with theoretical predictions.

Application of pattern recognition techniques to qualitative electrochemical analysis: Part I. Feature extraction of non-linear characteristics of the electrode process by the two-dimensional fast Hadamard transform

Abstract The feature extraction on non-linear characteristics of the electrode process is described. A model consisting of a linear element and a static non-linear element (ZNL=zero-memory non-linear system) is used to acquire the representation of the electrode process, from which the features of the electrode process should be extracted. That is, the electrode process is assumed to be composed of two processes, a solution process which has a dynamic characteristic due to the accumulation of materials in solution, and a surface process which has a non-linear characteristic like a kind of Butlers relation, etc. Previous work showed that a linear diffusion model with and without pseudo-first order chemical reactions made it possible to obtain the representation of the former process as a cross-power-spectral pattern (linear transfer function) between the current ( I ) and the surface concentration ( c ). For the latter process, it should be pointed out that its non-linear characteristics are nearly static due to the absence of material accumulation along the normal direction to the surface at the electrode surface. On the basis of this static non-linear model, this paper shows that the surface process can be represented by a pattern of a static curved surface, E - I - c ( E = electrode potential) obtained by use of the computational measurements of the surface concentration. A two-dimensional fast Hadamard transform achieved high information compression in the feature extraction of the observed E - I - c pattern.

Application of a microcomputer for the cross-spectral analysis with pseudorandom signal in electroanalytical chemistry

Abstract A digital memory device and a microcomputer are introduced to calculate correlation functions and Fourier transform in voltammetric measurements. Typical cross-spectra for simple diffusion and kinetic processes are obtained. The fast Fourier transform (FFT) modified for microcomputers was used for speed-up of the calculation. The cross-spectra obtained gave information about the electrode process such as the pattern of the accompanied chemical reaction and the kinetic parameter of the chemical reaction.

Measurement of Retention Indexes on n-Alkane Scale in Reversed-Phase Liquid Chromatography and their Prediction from Molecular Structures

Abstract A method was proposed in which the retention indexes (RI) defined on the n-alkane scale were measured by using 1-phenylalkane homologous series as reference compounds. Good agreement was observed between the RI values obtained with this method and those determined using n-alkanes as the reference. An attempt was made to predict the RIs based on the additivity for the constitutive atomic groups. The RIs were estimated with considerable accuracy by using increments of substituents themselves and positional increments between substituents. It was possible to distinguish methylnitroaniline isomers by comparison of the calculated RI values with the observed values.

Correlation between Electron Capture Response and Chemical Structure for Sulfur Compounds

Abstract The temperature dependence of the electron capture process was investigated for a series of divalent sulfur compounds. The electron affinity and/or the activation energy for the electron capture reaction were calculated for individual compounds by plotting In KT3/2 vs. 1/T, where K is the electron capture coefficient and T is the absolute temperature in the detector. The correlation between these values and chemical structure was discussed by means of 3d orbital resonance of the sulfur atom.

Analog feedback linear learning machine applied to the peak height analysis in staircase polarography

Abstract An analog feedback linear learning machine (ALLM) was applied to the quantitative and simultaneous determination of Pb 2+ , Tl + , Cd 2+ and Zn 2+ in 1×10 −1 M potassium nitrate solution by use of staircase polarography. Each concentration of these species could be determined with an accuracy of ±10%, though their peaks, especially those of Pb 2+ and Tl + , severely overlapped each other.

Application of pattern recognition techniques to qualitative electrochemical analysis: Part II. On-line measurements of double-layer capacity by the superimposition method and adaptive compensation of charging current by the capacitance multiplier

Abstract A random voltage signal with a larger amplitude for the faradaic electrolysis, on which a high-frequency small sinusoidal ac voltage signal is superimposed, has been used as a input signal. The response current of the ac voltage signal consists of the charging current. Gain values and phase values of the electrochemical double layer, which are obtained by comparison of input and output of the high-frequency signal, are located against the sample value of the electrode potential ( E ) at each moment using a microcomputer, and the images of both E−C dl (gain) and E− (phase) patterns come out gradually in the memory of the microcomputer, where C dl is the double-layer capacity and θ is the phase difference. The gain values are used for the control of the capacitance multiplier, which becomes an accurate and real-time simulator of the practical electrochemical double layer at the different electrode potential. An adaptive and real-time compensation of the charging current has been achieved merely by the analog subtraction of the current flowing through the capacitance multiplier (only the low-frequency potentiostatic signal is applied to its input terminal) instantaneously from the low-frequency response current.

Application of pattern recognition techniques to qualitative electrochemical analysis: Part III. Data compression of non-linear static characteristics of the electrode process

Abstract By the two-dimensional fast Hadamard transform, non-linear characteristics of the electrode process have been compressed into a small matrix which can be fed to an automatic retrieval system or a learning machine.

Selective gas-chromatographic detection using an ion-selective electrode-II Selective detection of fluorine compounds.

Components in samples are separated on a gas chromatography column using hydrogen as carrier gas. The individual components from the column are passed through a platinum tube heated at 1000 degrees , where they undergo hydrogenolysis, and fluorine compounds are converted into hydrogen fluoride. The hydrogen fluoride is dissolved in a slow stream of an absorption solution, and the fluoride ion concentration in the resulting solution is monitored in a flow-cell with a fluoride ion electrode. The potentiometric output of the cell is converted into a signal, which is proportional to the concentration of fluoride ion, by an antilogarithmic converter, and recorded. The response of the detector to fluorine compounds was about 10,000 times that to an equal quantity of other organic compounds, and 5 x 10(-11) mole of fluorobenzene could be detected.