Peixin He James P. Avery Larry R. Faulkner
Instrumentation
Department of Chemistry University of Illinois 1209 West California St. Urbana, Ill. 61801
Cybernetic Control of an Electrochemical Repertoire There has been such diverse growth in the means of approaching problems in analytical chemistry that we now find ourselves in need of new methods for controlling experimental power. The older modes of control that have brought about the growth itself are excellent for ensuring quality within a single format of experimentation, such as differential pulse polarography,
atomic absorption, or reversed-phase liquid chromatography, because they concern details of measurement. For three decades we have witnessed a campaign for precision and speed, in which the goals have been to identify factors affecting these properties of measurement in all sorts of experiments, and to control them by improved design of hardware, by servo
systems, by analog feedback, or by digital supervision. The era now drawing to a close has been regarded as the "electronic age" of chemical instrumentation, but electronics has really only served as a primary agency of control in an age of measurement. The root of new power in analytical chemistry is variety itself, that is, in having the ability to pursue several
Digital Plotter
Keyboard
Real-Time Clock RS-232 Interface
Video (Including 6K RAM)
Cell Control
Connect/Disconnect Dislodge Dispense Purge
Function Generator (16-Bit)
Timers Counters DAC
Potentiostat ±12V, ±300mA
i/E and Integrator
Processor (8O80orZ80) 36KROM (Control Software)
Printer Interface 22KRAM (Data)
Scales
ADC (12-Bit)
Figure 1 . Block diagram ot the instrument Blocks in blue are functions available on commercial boards. Remaining blocks show functions implemented on our boards 0003-2700/82/A351-1313$01.00/0 © 1982 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982 ·
1313 A
lines of attack on a chemical problem. Advanced concepts of control will be needed as instruments capable of coordinated investigations come to pass. Their advent will very likely alter the practice of analytical chemis try as substantially and as quickly as the campaign for precision and speed did. The era now beginning will be the age of coordination and interpreta tion, and its chief agent will be the computer. In this article we deal with these ideas, but within the specific context of electrochemical instrumen tation. The starting point is the prem ise that most chemical systems of elec trochemical interest ought to be exam ined by several techniques. In analytical applications, particu larly in the development of methods, one gains greater command of a sam ple by examining it by various types of pulse voltammetry, possibly by ac vol tammetry in any of several forms, and perhaps by one or more stripping pro cedures. The goal, of course, is to find the combination of conditions that leads to optimum sensitivity, preci sion, and immunity from interference. Optimizing conditions and recognizing interference demand the ability to change conditions, both within the cell and without. Accordingly, flexibility in the format of electrochemical exci tation and observation is required. Likewise, in diagnostic applications, different techniques tend to highlight different aspects of a mechanism. For an overview of chemistry, cyclic vol tammetry is powerful, but normal and reverse pulse voltammetry, rotatingelectrode methods, or chronocoulometry may provide simpler means for ob taining quantitative evaluations of pa rameters; and bulk coulometry is in valuable for determining η values. Thus we arrive at the concept of repertoire. Power in an electrochemi cal laboratory arises from an ability to bring a variety of techniques to bear on a problem. With current commer cial instrumentation, such power is out of reach in all but the most elabo rately equipped laboratories because individual experimental stations must be dedicated to each family of related methods. Alternatively, one can use very complex instruments that can be interconnected in various ways to carry out different types of experi ments. The impediments to imple menting a repertoire in hardware are almost prohibitive. In usual practice, therefore, studies are made by the one or two methods that are readily avail able in the laboratory at the time of investigation. Ideally, one would have a full range of options on a single instrument. There should be a simple, common style for selecting and setting up the experiments, regardless of experimen
tal mode; and the time needed to switch between modes ought to be negligible. The only realistic means for approaching this ideal is to place the entire repertoire under the charge of a computer. It must have full control of the potentiostat and cell by an auto mated switching network; it must offer a full range of excitation wave forms and schemes for acquisition of data; and it must possess a faculty for decision and communication, so that it is able to interact simply and in a "hu mane" way with the person supervis ing the investigation. The cybernetic solution to this problem in instrumentation succeeds, as we show below, precisely because it allows simplicity to coexist with vari ety. Outstandingly simple control is maintained over a great diversity of experimental methods and time scales. We expect to find that this coexistence will change the way in which electrochemical investigations are conceived and carried out.
A Working Example We have constructed a cybernetic potentiostat on the basis of these ideas. The design is shown schemati cally in Figure 1, and a photograph of the entire apparatus is available at the end of this article. The heart of the device is a commercial Intel SBC-80/ 10B single-board computer, which su pervises all operations. It operates in a standard Intel Multibus chassis, by which it interacts with additional memory and with three additional, custom-designed boards that carry the potentiostat, hardware for synthesiz ing waveforms for the potentiostat, circuitry for acquisition of electro chemical responses, apparatus for switching cell and scale connections, a controller for video display, and cir cuitry for automatic compensation of cell resistance. Details will be provid ed elsewhere (1). The operator receives information through an integral 5-in. video screen capable of presenting text and 192 X 256 point resolution graphics. Com mands are entered through a standard keyboard. Permanent copies of graph ical data are available at high resolu tion from a digital plotter or at low resolution from a dot-matrix printer. The figures shown in the remainder of this article are photographs of results from the high-resolution plotter. Control of all functions is exercised through software resident in 36 Kbytes of read-only memory (ROM). The remaining 28 Kbytes of memory exist as random-access storage for data and other temporary informa tion. Of course, our major contribution is the development of the software in ROM, and the bulk of the remaining
1314 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
Table I. Electrochemical Repertoire of the Instrumei Pulse methods
Differential pulse polarography and voltammetry Normal pulse polarography and voltammetry Reverse pulse polarography and voltammetry Square wave polarography and voltammetry Tast polarography Stripping methods
Differential pulse stripping Square wave stripping Linear sweep stripping Sweep methods
Linear sweep voltammetry Cyclic voltammetry ac methods
ac polarography and voltammetry Phase-selective ac polarography and voltammetry Second-harmonic ac polarography and voltammetry Miscellaneous
Chronocoulometry Bulk electrolysis with coulometry Electrocapillary curves Automatic measurement and compensation of resistance
discussion concerns its design and op eration. Our work is built upon earlier developments by Anson, Bond, Lauer, the Osteryoungs, Perone, Smith, and their co-workers, who laid the founda tions of computer-controlled electro chemical instrumentation (2-12). More recently there has been interest in adapting inexpensive microcompu ters, including personal computers, to electrochemical purposes (13-17). Our work is, of course, an extension of these earlier efforts by others; how ever, we have brought something new to the field by full integration of all control circuitry into the apparatus and by our stress on richness in reper toire. Finer details of our software will be covered in a forthcoming publica tion (1). There are actually two ver sions: one for the 8080A microproces sor and the Intel SBC-series boards, the other for a set of boards, based on the Z-80 microprocessor, which we de veloped to operate in the Intel chassis. The instrument contains control circuitry and software that make it fully compatible with the static mer cury drop electrode (SMDE) produced
by EG&G Princeton Applied Research Corporation. In addition, there are a real-time clock and a set of interfaces to external devices such as printers and control terminals that are of occa sional use, but are not of concern here. The potentiostat has a standard adder design and is programmed by the output of a 16-bit DAC. Step and pulse measurements are possible on time scales from a few milliseconds to several seconds; cyclic and linear sweep voltammetry can be done at rates up to 50 V/s; and ac voltamme try is possible at 10-250 Hz. The full repertoire is shown in Table I. One has access to almost the complete range of electroanalytical methods that can be carried out with a single potentiostat. Many of the meth ods are effective either in a "polarographic" mode, with a conventional DME or with the SMDE ordered to produce new drops periodically, or in a "voltammetric" mode, for use with conventional stationary electrodes or with the SMDE ordered to hold a sin gle drop for the entire experiment. An important feature of the instru ment is a provision for automatic com pensation of cell resistance. Through software, the system first makes an ac tual measurement of the uncompen sated resistance in the cell; then it de cides the maximum degree of compen sation that can be prudently attained by positive feedback. The decisions are made on the basis of the responses of the actual cell to small pulses in po tential. The apparatus has the ability to switch stabilizing elements into the feedback loop, if it regards them as necessary for stability at high degrees of compensation. The potentiostat is never allowed to break into oscillation; nonetheless, full compensation is usu ally possible. There is also a separate repertoire of display and plotting operations. Re sults can be examined smoothed or unsmoothed, as averages of multiple runs, as differences between sample and background voltammograms, as first or second derivatives, as magni fied views of data in specified poten tial ranges, or as plots of individual sweep segments in multicycle voltam metry. Any data point can be read out numerically, and one can obtain par tial interpretation of results, as slopes and intercepts of Anson plots (18) of chronocoulometric data, or as peak currents and potentials or wave heights and half-wave potentials for all types of voltammetry. All inter preted results of this type are achieved by handling baselines exactly as an electrochemist would handle them, even for reversal currents in cy clic voltammetry. Many of these modes of display and interpretation are illustrated in this article.
26-FEB-82
10:13:26
ELECTRDCAPILLARY CtJRUE MEASUREf-lENT
EXP. CONDITIONS; INIT etmUI- 200 FINAL E[mU)- -12CC POTENTIAL INTERUPLimUl- SO SAMPLE NUMBER- 1
E(UGLT) Figure 2. Electrocapillary curves recorded at the SMDE Triangles are for a solution of 5 X 1Cr4 M AQDS in 0.1 M HN03. Circles are for 0.1 M HN03 without AQDS
All experiments are set up and run in a common format. Once the opera tion mode is selected, a series of queries is made about the details of the experiment. Only essential infor mation is requested. After the setup is complete, a separate command orders the experiment to be run; then the re sults are displayed. With appropriate commands, they can then be analyzed, replotted, or the experiment can be re peated. Some of the parameters can be changed, or a new mode of operation can be invoked. Some Results
An example of the versatility of the system is shown in Figures 2 and 3, which contain a sequence of plots from a set of diagnostic experiments on a deaerated solution of 2,6-anthraquinone disulfonic acid (AQDS) at 5 X ΙΟ" 4 Μ in 0.1 M HNO3. The working electrode was the SMDE, modified slightly to permit automatic recording of electrocapillary curves like those shown in Figure 2. The pair of curves available there shows immediately that the compound of interest, or the products of its reaction at the elec trode, are adsorbed at potentials more positive than —0.7 V vs. Ag/AgCl, whereas at more negative potentials these species are not adsorbed. The slow-sweep cyclic voltammogram in Figure 3a shows that AQDS is reduced between +0.1 and —0.3 V in a pattern suggesting that the process in volves chemical reversibility, but has complex dynamics. The pair of spikes near 0.0 V strongly indicates that ad sorbed AQDS is reduced there to an adsorbed product, and the broader peak near —0.2 V indicates the reduc
1316 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
tion of diffusing AQDS in solution. Taking Figures 2 and 3a together, it is clear that oxidized AQDS is surface bound at potentials more positive than 0.0 V, and that the reduced form is surface bound between 0.0 and —.0.7 V. Beyond —0.7 V the reduced form desorbs and exists near the electrode only in solution. Figure 3b is a fastsweep cyclic voltammogram that con firms the assignments of the features in Figure 3a by the much stronger sweep-rate dependence of the peaks at 0.0 V by comparison to the peak at - 0 . 2 to - 0 . 3 V. The bump at -0.7 V in the negative sweep is probably caused by a change in capacitance ac companying the desorption indicated in Figure 2. An important strength of this instrumental approach is the ease with which data can be taken over a wide range of time scales, without the artificial limits often imposed by re cording equipment. Figure 3c is the chronocoulometric response to steps from +0.2 to —1.0 V and back to +0.2 V. This technique is especially powerful for quantifying the amounts of species bound to surfaces. However, it is inconvenient to use without a computer, because data are examined by plots on square-root-oftime axes (Anson plots) like those shown in Figure 3d for the data in Fig ure 3c (18). The difference in inter cepts of plots for the first and second parts of the experiments (upper and lower lines in Figure 3d) provides, es sentially, the difference in amounts of oxidized and reduced forms that are surface bound at the initial and firststep potentials, respectively. From the electrocapillary curves in Figure 2, we have already learned that the reduced
(a) 26-FEB-B2
10:16:25
CYCLIC UOLTBIIMETRY
EXP.
(b) CONDITIONS:
INIT EtmUJ- 200 HIGH ei™ui- 200 LOW ElmUl- -1200 U ImU^SCCI- 100 INIT P'N- NEGATIVE SWEEP SEGMENTS- 2 SAMPLE INTERUBL(mU.'SPL)-
26-FEB-82 CYCLIC
10:19:32 EXP. CONDITIONS:
UOLTBnMETRY
INIT E l m U ) - 200 HIGH E(i»V)- 200 LOU E U U l - -1000 U («U^SECl- 5120 INIT PSN- NEGBTIUE SWEEP SEGMENTS- 2 SBMPLE INTERUBLInU/'SPL)-
1
1
EIUOLT! EtUOLT)
(C)
26-FEB-B2
10: 2 2 : 30
(d) 26-FEB-82
CHRDNOCOULOMETRY
10:22:30 EXP. CONDITIONS:
CHRONOCOULOtlETRY
INIT EfmVl- 200 FINAL EtmUI- -10C0 PULSE WIDTHImSEC)- 250
EXP. CONDITIONS: I N I T ElntUI- 2 0 0 FINAL E i m U Î - - 1 0 0 0 PULSE W I D T H U S E C I - 2S0
FORUftRD STEP: SLOPEI»C^mSEC"*>- 0.1330 INTERCEPT1»CI- 1.0630 CORRELATION- 0.9997
REVERSE STEP: SLOPE[MC^mSEC"*J- 0.1441 INTERCEPTUCI- 0.4041 CORRELATION- 0.999B
TIME(mSEC)
(β) 26-FEB-B2 B.C. POLBROGRBPHY
10:28:03
(f) 26-FEB-82
EXP. CONDITIONS:
10:28:03 EXP. CONDITIONS:
B.C. POLBROGRBPHY
INIT EinUJ- 200 FINAL EtmUl- -1000 υ tmU^SECl- 4 B.C. BMPLITUDEImUl- 10 FREQUENCY(HZ)- SO CROPPING T I M E I m S E O - 1500
INIT ElmUl- 200 FINBL ECmUJ- -1000 U tBiU/SECI- 4 B.C. BnPLITUDEtmUI- 10 FREaUENCYIHZJ- SO DROPPING T I M E U S E C I - 1 5 0 0
EXP.
E(UOLT)
RESULTS:
PEBK POTENTlBLtwUi- + 2 0 PEBK CURRENT I B ) - 4.Θ2Β1Ε - 6
ECJOLT)
Figure 3. Various electrochemical responses at the SMDE for 5 X 10~ 4 M AQDS in 0.1 Μ ΗΝ0 3 (a) Cyclic voltammetry at ν = 100 mV/s. Cathodic currents are up. (b) Cyclic voltammetry at 5120 mV/s. Note change in current scale, (c) Chronocoulometric charge-time curve for step width of 250 ms. (d) Anson plots of data in (c). Top curve is for forward step and is charge vs. f1'2. Bottom curve is for net charge in the reversal phase vs. a more complex square-root-of-time function, (e) AC polarogram at 50 Hz. (f) Plot of part of the data in (e) at higher resolution
form is not adsorbed beyond -0.7 V; hence the choice of -1.0 V for the step potential in chronocoulometry allows us to attribute the difference in inter cepts in Figure 3d wholly to the amount of surface-bound AQDS at the initial potential. In Figure 3e, one sees an ac polaro gram of the AQDS system. Prominent
features are the peak for the surfacebound couple near 0.0 V and a broad maximum between —0.6 and —0.9 V, probably associated with capacitive changes induced by desorption of the reduced species. Figure 3f contains a closer view of the desorption peak in the same set of data. This sequence illustrates the rapid
1318 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
diagnosis of behavior that one can carry out when it is possible to exam ine different aspects of a system by optimal methods. The real-time clock readings on the plots in Figures 2 and 3 show that all of the measurements were made and plotted in about a 20min span. The plotting of high-preci sion graphs required 14 min of this pe-
For Strength, Durability, Inertness and Reproducibility Use the New GLT Packed Column From SGE
(a)
27-FEB-82
10:18:13
D1FFERÉN71RL PULSE POLRRDGROPHY
EXP. CONDITIONS: IN1T EtmUt- -200 FlNRL ElmUl- -1500 UlmU/SEO- 4 PULSE RtlPLITUDEImUl- 50 PULSE UIDTHImSECI- 50 PULSE PERIOD(mSECt- 10OO
EXP. RESULTS: PEAK POTENTIRHinUl- -40Θ PERK CURRENT[pi- 4.0393E -Θ PEAK PQTENTlfiLCmUl 720 PERK CURRENTtfll- 1.4S12E - 7 PERK POTENTIOLImUl- -1008 PERK CURRENT(flΙ- 6.73Θ5Ε - β PERK POTENTIPLimUl- - 1 2 7 2 PERK CURRENTÎR1- 9.4549E - β
(b)
27-FEB-82 PHASE S E L E C T I V E
1 1 : 56: 05 R.C.
POLfWOCRPPHY
The New GLT Packed Column Has It All S T R E N G T H The GLT Column is protected by a sleeve of stainless steel which allows the borosilicate glass lining to stand up to the toughest laboratory conditions. D U R A B I L I T Y The GLT effec tively eliminates the problem of col umn fragility without sacrificing inertness REPRODUCIBILITY Through the use of consistent column pack ing techniques and rigorous quality control procedures, a high degree of column to column reproducibility is insured. I N E R T N E S S The GLT exhibits extremely high levels of inertness from batch to batch . . . at a level which is equal to the best all glass column. For the complete GLT story con tact your nearest SGE sales office.
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EXP.
CONDITIONS:
INIT Ε I « V I - -ZOO FINAL E l p i V I - - 1 5 0 0 UteO^SECÏ- 4 fl.C AnPLITUDECwUI- 25 FREOUENCYtHZl- 50 PHASE SHTFTtOECREEf- β DROPPING TlrlElmSECJ- 1600
EXP. RESULTS: PEAK POTENTIftL(»iU1- - 6 8 0 PEAK CURRENT(fil- 1.9BZ4E
E(UOLT)
Figure 4. Polarograms at the SMDE of a solution containing 1 X 1 0 - 5 M analytes in 1 M ammoniacal buffer Peaks, from left to right, are for Cu(ll), Cd(ll), Ni(ll), and Zn(ll). (a) Differential pulse polarogram. (b) Phase-selective ac polarogram
riod, so the actual experimental time was only about 6 min. Even in wellequipped conventional laboratories, it would be difficult to complete this work in a day—if the measurements could be fully carried out at all. Par ticularly in the early stages of an in vestigation, when one is attempting to gain a qualitative feeling about a sys tem in advance of detailed work, it is very convenient to dispense with highprecision plotting and just "converse" with the system by examining its re sponses in a great variety of experi ments on the video monitor. It is easy to obtain results from 20 to 30 experi ments in half an hour in this manner. The real benefit of such speed is that one is permitted to concentrate on the chemistry. Figures 4-6 illustrate features that are useful in analytical applications. In Figure 4a, one can see the differen tial pulse polarogram of a solution of Cu(II), Cd(II), Ni(II), and Zn(II) all at 1 Χ Ι Ο - 5 Μ in ammoniacal buffer. The instrument determines peak positions and heights for all four components, as shown. A rather different view of
CIRCLE 188 ON READER SERVICE CARD
1320 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
the same system is found in Figure 4b, which contains a phase-selective ac polarogram. The peaks for Ni(II) and Zn(II) are suppressed because they are less reversible than those for Cu(II) and Cd(II). If one were interested in quantifying all four species, then dif ferential pulse polarography would be the method of choice, but if the inter est were only in the level of Cd(II) in the presence of large, interfering con centrations of Ni(II) and Zn(II), then the tendency of the ac method to sup press the interferents would be useful (19). For any given purpose, one might find this solution examined op timally by either of these methods, or by others such as square-wave polar ography, second-harmonic phase-se lective ac voltammetry, stripping methods, or even a first-derivative plot of the normal pulse polarogram. The point is that with a nearly com plete repertoire, one can quickly ex amine the possible approaches to find the optimal one. In analytical applications, various options for processing information can be especially useful. Figure 5 is an il-
(a)
27-FEB-82
23:31:30
D I F F E R E N T I A L PULSE S T R I P P I N G
UDLTfVtflETRY
EXP. CONDITIONS: INIT EtnUl- -300 FlNRL EIwU)- Ο U(»U/SECi- 1C PULSE AMPLITUDE I » W - SO PULSE PERlODImSECl- SOC DEPOSIT TIMEISEO- SO
EXP. RESULTS: PEAK POTENTIAL l«.Ui« -325 PERK CURRENT{RJ- I.C7S1E -
(b)
27-FEB-B2
23:45:29
DIFFCRENTIBL PULSE STRIPPING UCLTWIOETRV
EXP. CONDITIONS: ΪΝ1Τ E i n U I - - 9 0 0 FINAL E l n U ) - 0 U(BIU/SEC1-
10
PULSE R H P L l T U D E f w U l - SO PULSE P E R I O D I m S E C J - 5 0 0 DEPOSIT T W E I S E C I - 6 0
EXP. RESULTS: PEAK P O T E N T I A L . ! » * ! ) - ~S\S PEAK C U R R E N T ( A ) - 4 . t B 0 3 E - Θ PEftK P O T E N T I A L ! * * ! ) - - 3 Z Û PEAK CURRENTtft>- 2 . 2 9 B 9 E - θ
lustration of blank subtraction. In blank 0.05 M K N 0 3 ) the differential pulse stripping voltammogram (Figure 5a) reveals a peak, probably due to Pb(II) present as a contaminant. In addition, there is an inconveniently sloping baseline in the region near —0.5 V, where a determination of Cd(II) might be made. This slope is apparent in Figure 5b, which contains the differential pulse stripping vol tammogram for a sample of Cd(II) and Pb(II), both at 5 Χ ΙΟ" 8 Μ in 0.05 M KNO3. Of course, the peak in the blank is also a serious interfèrent to the response from Pb(II) in this voltammogram. Since the instrument can store a blank voltammogram and subtract it from another upon command, one can readily obtain the corrected responses shown in Figure 5c for the sample of Cd(II) and Pb(II). The improvement in the baseline and the importance of correcting the peak for Pb(II) are clear. A related form of information processing is found in Figure 6. Curve (a) is the differential pulse polarogram for a solution of 5 Χ ΙΟ" 8 Μ Cd(II) in 0.05 M KC1. The peak for Cd(II) is evident, but it is superimposed on such a strongly sloping baseline that the eval uation of its height and position by automatic routines becomes difficult. A simple subtraction of a ramp flat tens the baseline [curve (b)], so that the peak stands out and is readily quantified. It is obvious from this fig ure that detection limits for differen tial pulse polarography can extend near 1 0 - 8 M on this apparatus. A View of the Future
(C)
27-FEB-92 DIFFERENTIEL
2 3 : 45: 29
PULSE S T R I P P I N G UDLTflMMCTRV ( 2 1
EXP. CONDITIONS: TNIT E l e U l - - 9 0 0 FINAL E l i e U l - 0 UtnUVSEC)- 10 PULSE R f 1 P L l T U D E ( « U l - SO PULSE P E R I O D t m S E C l - SOO DEPOSIT T I M E ( S E C ! - 6 0
EXP. RESULTS: PEAK POTENTIAL ! • * < ) - - 5 1 5 PEAK C U R R E N T I A ) - 3 . 6 C C S E - β PEAK P O T E N T I A L ! · * ' ) - - 3 2 0 PEAK C U R R E N T ( R ) - 1 . 1 6 Z 8 E - 5
EtUOLTl
Figure 5. Differential pulse stripping voltammograms at the SMDE Note differences in scale between frames, (a) 0.05 M KNO3 blank, (b) 5 X 10~8 M Cd(ll) and Pb(ll) in 0.05 M KN0 3 . Peak for Cd(ll) is at right, (c) Difference between (b) and (a) 1322 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
Even though we have dealt specifi cally with electrochemical instrumen tation, we want to close by stressing the generality of the idea that a large repertoire, invoked conveniently, is a new form of experimental power that only now is becoming possible. Instru mentation similar to our electrochemi cal apparatus could be imagined read ily, for example, for chromatography, mass spectrometry, or optical spec troscopy. To some extent, it already exists for NMR. It is quite clear that developments along these lines will be very important to analytical chemistry in coming years. Since the kinds of in struments that we are discussing here differ qualitatively from their prede cessors, it is perhaps a good time to consider a generic term to describe them. The major new concepts in these in struments concern control, automatic interpretation, decision making, com munication, and interaction with an operator; hence we suggest that the adjective cybernetic will serve as an accurate, succinct descriptor. Vander Velde (20) defines cybernetics as the
Laboratory Automation Update
(a)
27-FEB-82
14: 48: 58
DIFFERENTIAL PULSE POLAROBRAPHY
EXP. CONDITIONS: I N I T ECnUl- - 3 0 0 FINBL El»l>>- - 8 0 0 UlnAI^SEO- 4 PULSE A M P L I T U D E C B I U ) -
SO
PULSE PERIODtnSECI- 1000
EXP. RESULTS:
(b)
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27-FEB-82
14:48:58
DIFFERENTIAL PULSE POLAROCRBPHY
EXP. CONDITIONS: INIT E(«iU>- -300 FINBL EleUl- -BOO UlmU/SECI- 4 PULSE AMPLITUDE («HI- SO PULSE PERIODImSECl- 1000
EXP. RESULTS: PEAK POTENTIAL li»U)- -S12 PEAK CURRENT(AI- 1.5249E -9
Figure 6. Differential pulse polarogram at the SMDE of 5 X 1 0 - 8 M Cd(ll) in 0.05 M KCI (a) As recorded, (b) Redisplayed after subtraction of linearly sloping baseline
"science of control and communication in all of their manifestations within and between machines, animals, and organizations." He goes on to say that in more common usage, the term "refers more specifically to the interaction between automatic control and living organisms, especially humans and animals." Lexicographers are willing to accept the adjective cybernetic as descriptive of things "relating to," or "involving" cybernetics. Thus, the language seems already to have a word to describe the kind of system we have in mind, and that word seems much more precise than the more vague terms that might be adopted from the literature, such as "computer controlled" or "automated." To refine this term, we propose that apparatus to be regarded as cybernetic instrumentation ought to offer four elements: • advanced communication and control systems especially designed to
CIRCLE 245 ON READER SERVICE CARD 1324 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
offer "humane" interaction between the apparatus and its operator; • an ability to interpret results, at least by partially reducing data; • an ability to pursue different courses of action selected from a repertoire; and • an ability to make decisions based on experimental results. The apparatus that we have described here offers all of these elements. Its least developed ability is in making decisions based on the outcome of its experiments, but a good example of such action is in its approach to the compensation of resistance. In general, researchers interested in analytical instrumentation have the understanding and technology to create cybernetic systems in which the first three attributes have been highly refined. The ability to achieve skilled decision making within an instrument, especially decision making based on growing experience, is poorly developed. When more is
Jewett contemporary styled
LABORATORY REFRIGERATORS & FREEZERS
References (1) He, P.; Avery, J. P.; Faulkner, L. R., in preparation. (2) Lauer, G.; Abel, R.; Anson, F. C. Anal. Chem. 1967,39,765. (3) Lauer, G.; Osteryoung, R. A. Anal. Chem. 1968,40(10), 30 A. (4) Perone, S. P.; Harrar, J. E.; Stephens, F. B.; Anderson, R. E. Anal. Chem. 1968, 40, 899. (5) Keller, H. E.; Osteryoung, R. A. Anal. Chem. 1971,43,342.
(6) Perone, S. P.; Frazer, J. W.; Kray, A. Anal. Chem. 1971,43, 1485. (7) Creason, S. C.; Hayes, J. W.; Smith, D. E. J.Electroanal. Chem. 1973,47, 9. (8) Glover, D. E.; Smith, D. E., Anal. Chem. 1973,45, 1869. (9) Smith, D. E., Anal. Chem. 1976,48, 221A, 517A. (10) Thomas, W. V.; Kryger, L.; Perone, S. P. Anal. Chem. 1976,48, 761. (11) Brumleve, T. R.; O'Dea, J. J.; Oster young, R. Α.; Osteryoung, J. Anal. Chem. 1981 53 702. (12) Anderson, J. E.; Bond, A. M. Anal. Chem. 1981,53, 1394. (13) Norris, Α.; Bond, A. M. Anal. Chem. 1980 52 367. (14) Anderson, J. E.; Bagchi, R. N.; Bond, A. M; Greenhill, H. B.; Henderson, T. L. E., Walter, F. L. Am. Lab. 1981, 73(2), 21. (15) Kryger, L. Anal. Chim. Acta 1981, 733 591 (16) Brown, O. R. Electrochim. Acta 1982, 27 33. (17) 'Price, J. F.; Cooke, S. L.; Baldwin, R. P. Anal. Chem. 1982,54, 1011. (18) Anson, F. C. Anal. Chem. 1966 38,54. (19) Bond, A. M. Anal. Chem. 1973,45, 2026. (20) Vender Velde, W. E. In "McGrawHill Encyclopedia of Science and Tech nology"; McGraw-Hill, New York, 1977; Vol. 3, p. 687.
Peixin He (foreground) is an ex change scholar on leave from his instructorship in the Department of Chemistry, Fudan University, Shang hai, People's Republic of China. He completed his undergraduate educa tion at Fudan University in 1976, then spent two years in graduate study there. In 1980 he came to the University of Illinois for a two-year period. His interests are in electroanalytical chemistry and in electro chemical instrumentation. James P. Avery (right) is assistant professor of chemistry, University of Illinois. He received his BS in com puter science from Michigan State
University in 1972 and his PhD in chemistry from the University of Illi nois in 1978. He recently joined the Department of Electrical Engineer ing, University of Colorado, as assis tant professor. His research interests are in the development of systems and languages for the automation of analytical instruments. Larry R. Faulkner (left) is profes sor of chemistry, University of Illi nois. He received a BS at Southern Methodist University in 1966 and a PhD in chemistry in 1969 from the University of Texas at Austin. His main interests are in electrochemis try and luminescence spectroscopy.
learned about the way to achieve it, there will be spectacular results. It is already clear that we are not far from seeing instruments that will carry out scientific investigations, not just mea surements. Acknowledgment We are grateful to the National Science Foundation for supporting this work through Grant CHE-8106026 and to the Fudan UniversityUniversity of Illinois Exchange Pro gram for extending a fellowship to one ofus(P.H.).
LAR 25B
5 Models to choose from 1 2 to 5 5 c u . f t . c a p a c i t y This n e w line of refrigerators and freezers is completely functional yet attractively con temporary in styling and finish. Exterior fronts are available in a choice of blue or tan gerine w i t h beige cabinet and illuminated interior. Both have stainless steel adjustable shelves interchangeable w i t h stainless steel drawers (optional extra). Thermal uniformity is maintained by automatic fan disconnect w h e n door is open. The blower-coil cooling system has automatic defrost. The auto matic condensate evaporator eliminates the need for plumbing. Both refrigerators and freezers can be equipped w i t h cylinder locks in door fasteners for safety.
LABORATORY REFRIGERATORS • w h i t e enamel interior* • uniform cabinet temperature (2° to 4 ° C) • quick temperature recovery • dual or single air circulation system
LABORATORY FREEZERS • stainless steel interior • uniform cabinet temperature of -18°C(0°F) • quick temperature recovery • dual or single air circulation system All refrigerator models are available w i t h glass doors. Pass-thru oper ation available for refrig erators and freezers. "Also available with stain less steel interior and ex terior finishes
J EWETT REFRIGERATOR
2 LETCHWORTH ST BUFFALO, N.Y. 14213
The Best of Both Worlds . . . individual Craftsmanship combined with Modern Technology CIRCLE 106 ON READER SERVICE CARD
1326 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
