| 摘要 |
A coulometric titrator for determining, at high accuracy and without time delay problems, small amounts of a specific ion in a solution by the addition of a reactive ion. A sensor provides a signal voltage representing the logarithm of the specific ion concentration to a differential amplifier which also receives as an input a signal from a reference electrode. The differential amplifier produces an error signal applied to a comparator and referenced therein to a certain reference voltage representing a desirable range of rates of change of the error output voltage. The comparator provides a sensor signal voltage representing the difference between the error signal and reference voltage. This sensor signal voltage is applied to an antilogarithm converter which produces an output signal that is proportional to the antilogarithm of the sensor signal voltage. The output signal is received by a reactive ion (silver metal) source means associated with a current source passing a unidirectional current flow between an inert cathode immersed in the solution and the reactive ion source means as an anode for the introduction of the reactive ion (silver) into the solution. As a result, the signal voltage representing the logarithm of a specific ion concentration changes at a constant rate with time, and the reactive ion addition changes in a logarithmically decreasing amount with time in the sample solution until the stoichiometric end point is approached. The present coulometric titrator incorporates (1) a reversing switch which changes the polarity of the measured cell potential to allow the instrument to perform coulometric titrations which have negative going voltage changes near the equivalence point; and/or (2) a slope adjustment which changes the slope of the anti-logarithmic function which allows practical coulometric titrations of systems where the voltage change with concentration is more or less than 60 mV per decade of concentration such as occur in 2 and 3 electron reactions and other more complicated chemical systems.
|
