INSTRUMENTATION by Ralph H. Müller
Electroanalytical Instrumentation INTERESTING to note from time I τtoistime the extent to which elegant instrumentation is being applied to the various techniques of present day ana lytical chemistry. We are almost com pletely convinced that the thought, time, and ingenuity expended is gov erned primarily by economic factors. The tremendous activity in the field of gas chromatography has made continu ing demand for better instrumentation. More recently, the highly exacting re quirements of quantitative microorganic analysis have been met by com pletely automated systems. In these systems about the only residual conces sion to classical techniques is the re quirement to weigh the sample on a microbalance. Even here, one manu facturer recommends the Cahn Electrobalance for that purpose and, in addi tion, uses its electrical output for other supervisory functions. These elegant devices, although ex pensive, are permitting impressive sav ings in time and money and, more fre quently than not, the precision is im proved. Widespread industrial use of such instruments and systems provides a profit which can support more exten sive instrumental development. We have the feeling that some of this finan cial autocatalysis may occur one of these days in electroanalytical instru mentation. The big question is—what development may hope to attain com parably widespread applicability ? Fundamental research in electroana lytical methods continues to proceed at a brisk pace. The fundamentals of the subject are well documented in text books such as Professor Paul Delahay's New Instrumental Methods in Electro chemistry [Interscience Publishers, New York, 1954] and in Professor J. J. Lingane's Electroanalytical Chemistry, 2nd Edition [Interscience Publishers, New York, 1958.] Inherently, electroanalytical methods are more directly amenable to extensive automation because the signals are al-
ready electrical and, as a rule, no spe cial transducers have to be developed. Once more, we suggest that electro analytical chemists give increasing at tention to organic systems. This is not to imply that the subject has been ig nored or completely neglected. Indeed, Lingane (loc. cit.) has described some thirty-four organic compounds or classes of compounds which have been analyzed by coulometric titration. The vast possibilities would still seem to be largely unexplored. POTENTIOSTATS MADE I N FRANCE
Some recent French developments have come to our attention which should be of interest to American ana lysts. The firm Tacussel Electronique, SOLEA, 2 et 4 rue Carry, Lyon/3, France, offers a wide range of electronic instruments primarily for electrochem istry. Some of these have no commer cial American equivalent. Of particu lar interest, we think, is their extensive line of potentiostats. These are avail able in a wide range of output power. Currents furnished can range from 0.5 to 50 amp. These instruments are fitted with carrier frequency amplifiers with a response time of 2-3 millisec onds. Regulation is better than ± 5 mv., typical values being ± 1 to 2 mv. They are particularly suitable for con trolled potential electrolysis. Other models are designed for fast response and use direct coupled amplifiers with a transistor power output stage. Mini mum time of response is of the order of 2-3 microseconds. They are particu larly suitable for plotting current as a function of voltage curves and for potentiokinetic studies inasmuch as the polarity of the controlling voltage and of the output voltage and current may vary independently without switching or change of connections. Still other models developed for oscillographic studies of very fast phenomena have response times of 0.2 to 0.5 //.sec.
The potentiostats have full protec tion against overload and short-circuits. Amplifier input impedance is 10,000 Μ Ώ, and noise and hum voltage is less than 2 mv. The controlling voltage ( ± 5 v.) is adjusted with a 10-turn heli cal potentiometer. Connections are available for external control of the in put circuit, and provisions are also made for superimposing an a.c. signal on the controlling voltage. At least four distinct units are avail able as pilot scanners for driving the input circuit of a potentiostat. One is a simple synchronous motor with startstop and reverse switch and available in 16 standard speeds for providing 1 v./min. to 1 V./24 hours. Other scanners have a helical poten tiometer driven by a reversible motor, the speed of which is controlled by an electronic servo amplifier affording speeds of 1 v./min. to 1 v./hour. A pulse generator is also available to drive a potentiostat by a pulsed controlling voltage. Positive or negative pulses can be generated with repetition rates of 10 c-10 kc. and with pulse widths of 1, 2, 5, 10, 50, 100, 200, 500 micro seconds and 1, 2, 5 milliseconds. Rise time is less than 1000 nanoseconds and the pulse amplitude is adjustable from 0-0.5 v. and 0-5 v. OTHER FRENCH ELECTROCHEMICAL INSTRUMENTS
Dr. Tacussel has developed many other instruments for electrochemical and electroanalytical use. Various models of logarithmic current measur ing equipment, electronic millivoltmeters, multimeters, milliammeters, pH meters, current integrators, and re lated instruments are available from SOLEA. An unusually wide array of special electrolysis vessels is listed. These instruments have had wide ac ceptance in France and other European countries in electroanalytical and gen eral electrochemical research.
VOL. 36, NO. 10, SEPTEMBER 1964
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