Transformationof Old Two-Electrode Polarographs into Three-Electrode Systems Old polarographic systems consist of a voltage generator (usually a motor-driven potentiometer), a low-pass filter with variahle time constant (the damping control), a potentiometric recorder with variable sensitivity for the current measurement (the current is passed through a resistor and the voltage drop is measured), a zero set control, and controls for the capacitance current compensation. At the time of their construction (1960-1970) electronic components were very expensive, and as a consequence these instruments are two-electrode systems with limited versatility. Many times they have better mechanical construction than modern instruments and can also withstand student use better. However, twa-electrode systems need a bulky calomel electrode, which is easily contami- ,,, ,.,l., n,n .,., nated. In addition, a two-electrode system is un- .-:mt;m?;:t~ suitable for work in nonaqueous solvents. In this work a simple circuit is proposed that can transform a two-electrode polarograph into a three-electrode system. After the modification, all of the controls of the oolaromaoh are functional. With this modifirstiod a p l l > y b reference electrode can be wed, and electrochemistry in nonaqueous sdventa can be carried out as well. As a counter electrode a spare pencil lead can be used (much cheaper than a commercial platinum wire electrode). In a three-electrode polsrography system an excitation signal, as well as the ramp potential, can be easily applied to the working electrode. A 20-mV ae voltagecan beepplied from the mains transformer, the aecurrent can beseparated from the dc current with a high-pass filter, then rectified and recorded. Thus a three-electrode system can easily be rendered suitable for ac polarography. This modification has been carried out in o w laboratory on two different types of polarographs: Metrohm Polarecord 261 and Radiometer Polsliter P04. In the case of the Radiometer P04, we did not encounter any difficulty. In the case of the Metrohm 261, the chasis ground was different from the instrument ground. (The ground of the circuit proposed has to be connected to the instrument (measuring ground).
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N. Papadopoulos and P. Llnardls Aristotelian University 01 TherSaloniki G-eece
Volume 66
Number 5
May 1989
419
