ABSTRACT
10.1 MICROPROCESSOR- AND MINICOMPUTER-CONTROLLED POLAROGRAPHS
Examination of the recent literature on virtually all polarographic techniques reveals that the use of the laboratory computer in polarographic analysis is becoming extremely common. Advances in electrochemical instrumentation are now closely following the state of the art in electronic components, and the use of digital circuitry to perform many functions previously undertaken in the analog format is becoming widespread. Clearly the most significant advance is the recent development of the integrated circuit microprocessor, now widely available at low cost and being incorporated into commercially available instrumentation. Along with low-cost integrated-circuit memories and digital-to-analog (D/A) and analog-to-digital (A/D) converters, the microprocessor makes possible the design of inexpensive instruments which are capable of closed loop control of data acquisition and reduction. That is, all facets of the experiment (for example, setting of scan rate, drop time, pulse height, potential increment, measurement of current or peak height, and calculation of concentration) are performed under computer control and without operator intervention. Figure 10.1 shows a “smart instrument” which uses microprocessor control of an analog potentiostat to perform differential pulse polarography, anodic stripping voltammetry, and a range of other techniques. Data manipulation procedures, such as rejection of data obtained from a bad drop, averaging of replicate measurements, calculation of peak height and position, background subtraction, and rescaling of the i-E curve, are also performed under microprocessor control. Some of these features are demonstrated in Figs. 10.2 to 10.4. Dessy and co-workers [1-3] have discussed microprocessors from the user’s point of view in several lucid articles, and their prognosis [3] is as follows:
There is little doubt that microprocessors are going to change the way instruments in research laboratories and analytical service areas are designed and operated and how they will interact with their operators. Within a few years most new equipment will be using microprocessors to acquire analytical data, perform small manipulations on the data base, and report the results.... The promise of complete instrument self-calibration and optimization and the potential to change instrument function drastically by simple changes in the operating program has been voiced.
FIGURE 10.1 A microprocessor-controlled polarograph. [Reproduced by courtesy of Princeton Applied Research Corporation (PAR Model 374 Polarographic Analyzer).]
FIGURE 10.2 Microprocessor-controlled polarographs and other "smart" instruments can average, autorange, and manipulate digital data to provide optimum presentation of curves. (Some manipulations on the differential pulse polarogram of librium are shown.) [Reproduced by courtesy of Princeton Applied Research Corporation (PAR Model 374 Polarographic Analyzer).]
FIGURE 10.3 Background correction is simple when data can be stored digitally. Polarogram of electrolyte is recorded and data are stored in memory. The result is then subtracted from polarogram of species to be determined. Example shown is the determination of arsenic(III) in 0.1 M HCl by differential pulse polarography , using a PAR Model 374 Polarographic Analyzer. With analog equipment, the same kind of experiment would require matched dme's and cells and could be achieved only with great difficulty. (see Chap. 3). (Reproduced by courtesy of Princeton Applied Research Corporation. )
FIGURE 10.4 By developing suitable software, digitally stored raw data can be manipulated in many ways before the final readout is displayed. The above curve may be produced void of bad drops, for example. Such a facility is available on the microprocessor-controlled PAR Model 374 Polarographic Analyzer. (Reproduced by courtesy of Princeton Applied Research Corporation.)
