Comparative study of a thin-layer cell for analysis of stationary and streaming solutions

A comparative study with a home-built Kissinger-type twin-electrode thin-layer cell has been made, with the cell either filled with quiescent solutions or used as a flow-through detector. In both modes the cell was polarized by a slow linear potential sweep. The current-voltage curves recorded showed a limiting current region in both cases, in spite of the different types of transport process (steady-state diffusion caused by the redox cycling effect of the counter-electrode in the quiescent solution and convective diffusion in the flowing solution). The sensitivities and also the lower detection limits were found to be nearly the same for the two different modes of operation of the same cell, for which an explanation is given. The main analytical advantage of the thin-layer twin-electrode cell filled with quiescent solution is that only a few mul of analyte solution are necessary for the measurement. It was proved experimentally that this type of cell, used as a flow-through detector, gives the expected limiting current, but this current is dependent on the cube root of the linear flow-rate, in agreement with Weber's theoretical prediction, rather than on the square root of the flow-rate (commonly quoted in the literature).     

Critical comparison of evaluation methods of potentiometric titration data using a microcomputer-controlled automatic potentiometric titration system

A microcomputer-controlled automatic potentiometric titrator withP controlled intelligent auto-sampler has been built for serial analysis. Controlling and evaluating programs have also been written. In order to use the most powerful evaluating method, a comparison was made between the methods. The data of the titration curves were obtained by the implicit relation characterizing the curve. The different evaluating methods were tested by using these data. The effects of random errors stemming from measurements were also investigated. The methods used were: two point differentiating formula, differentiation of interpolating and smoothing spline functions, the Gran method, and implicit regression with the Gauss-Newton-Marquardt method. Regression is outstanding among the methods, but it needs much more computing time compared with others. The second-best method is the differentiation with smoothing spline function with end point determination based on finding the sign reversal of the second derivative. This method is much faster than regression.     

IBM PC-based multipurpose data-acquisition system for thermal analysis

A multipurpose data-acquisition system based on IBM PC or compatible computers has been developed for analog thermoanalytical equipment (especially for the Mettler TA 1 and TA 2 and Derivatographs). The system is versatile, easily tailored to specific requirements, and permits multitask operation, i. e. the collection of data from current experiments and the evaluation of results from previous experiments simultaneously.

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Zusammenfassung Basierend auf IBM PC oder kompatiblen Computern wurde ein Mehrzweck-Datenerfassungssystem für analoge thermoanalytische GerÄte (besonders für Mettler TA1 und TA2 und Derivatographen) entwickelt. Das System ist vielseitig, kann spezifischen Anforderungen leicht angepa\t werden und erlaubt den Foreground-Background-Betrieb, d.h. es können gleichzeitig Daten eines laufenden Experimentes erfa\t und Daten früherer Experimente ausgewertet werden.