Instrumentation Ralph H . Muller, Muller Reseorch and Development Corp., P. 0 . Box 6 157, Santa Fe, N. M.
P
RACTICALLY
EVERY
BRASCH
Of
analytical chemistry discussed in this series of reviews is concerned, in part, with new instruments, devices, and techniques for improving the speed and precision of the respective methods and are appropriately covered in these reviews. This report attempts to cover some of the more general aspects of instrumentation published between April 1960 and February 1964 and to direct attention to developments, some of which have not yet found analytical application. There are quite a few of these but their active study and development has been in the hands of physicists and engineers having no interest in analysis. For many years, electronics has played a dominating role in the instrumentation of interest to analysts. It is now undergoing a revolution, many aspects of which are almost incomprehensible to the analyst. The implications, as far as the analytical applications are concerned, are equally incomprehensible to the electronics experts. This has to do with the unremitting effort to produce electronic devices \\hich are smaller, compact, and increasingly reliable. Partly as a result of attempts to make electronic instruments for space vehicles small, free of hostile environmental conditions, and almost, fool-proof, there has been a continuing effort toward miniaturization. The background for these developments m s established in the early fifties by the advent of transistors and related solid-state devices. With construction and assembly techniques conducted under lowpower microscopes and in antiseptic environments, these attempts to produce the electronic “multum in parvo” were eminently successful and impressive. For some time, however, despite such techniques as electron-beam welding, preferential evaporation techniques, and other micro methods of fabrication, electronic engineers became increasingly aware of what they call the “tyranny of numbers.” This means, very simply, that, if the best resources of micro fabrication techniques are used to assemble a conventional circuit array, one approaches the point where the performance of a multitude of functions begins to be beset by decreasing 140 R
ANALYTICAL CHEMISTRY
reliability. Stated in another and more precise way, for a given procedure in miniaturization, there is a finite number of circuit elements and components which can be accornmodated in a given space. This, then, is an ultimate limit unless alternative approaches can be discovered. This has already been attained in a field termed microelectronics. most unusual treatise has appeared edited and co-authored by Edward Keonjian (20). The book is unusual in that editor. cooperating authors, and the publisher. have endeavored to produce a comprehensive survey of a field, and one in which much of what is already written will probably be ancient and out of date before a second printing is required. This treatise includes basic considerations in microelectronics, discrete component parts, thin film circuits, and semi-conductor integrated circuits. I t is the latter nhich offers the promise of a possible escape from the “tyranny of numbers.” In conventional electronics, whether on the macro or micro scale, one is concerned with an assembly of tubes or transistors, resistors, capacitors, inductors, and all the associated wiring. The revolutionary deviation, as exemplified by the functional or integrated circuit, is a solid state device in which all these elements are incorporated in a tiny element, the molecular or interfacial portions of which are equivalent to the conventional components including the wiring. The concept is not too difficult to comprehend because we have an ancient example a t hand. The piezo-electric c r p t a l , properly cut and fitted with electrodes, can act as a precise and frequency-controlling oscillator. As such. it is equivalent to an LC circuit and ITith Some necessarily-associated resistance R. Yet, nowhere in thiq quartz crystal is it possible to point to a region which represent.. either resistance, inductance, or capacitance. Ai recent accomplishment, described only as a news item (I@, is a single unit integrated circuit designed as a hearing aid. I t i q a 6-transistor, 16-resistor amplifier unit which performs as well as a printed circuit unit and is more reliable. I t is one-tenth the qize of a match head. The small dimenqion, for such versatility, is not of paramount
importance. The greater significance lies in the achievement of functional behavior in a tiny, single unit, completely foreign to the conventional array of wires, tubes and similar components. Another development of long standing service has, curiously enough, discovered no application in analytical instrumentation-at least to the author’s knowledge. This is the highlycomplex and highly-developed technique of magnetic tape instrumentation. A recent monograph by Davies ( 5 ) discusses the contemporary status of recording techniques. This is complete in all the mechanical, electrical, electronic, and acoustical phases of the method. Almost 100 references are given on scientific and technical applications of tape recording. A s might be expected, most of these are related to sound reproduction. dictating machines, and, in the technical matters of telemetry, computers, and space vehicle monitoring. Perhaps, some enterprising young analyst will esamine a 20-dollar transistorized tape recorder and find a way to record and play back data of analytical importance-instead of developing a ten thousand dollar instrument to perform a 10-cent titration automatically. In the latter connection, two monographs of fairly recent vintage, (8, 16) describe potentiometric, photometric, coulometric, and thermometric titrations as well as several automatic process monitoring devices. Circuit analyses and appraisals are given together with specific applications. AIthough some half dozen autotitrators are commercially available, it seems to be the opinion of both authors that no completely satisfactory solution of the problems has yet been attained. particularly if one considers speed, convenience, cost, and attainable precision. The author would suggest that an extremely practical appraisal of the autotitrator problem is badly needed preferably by industrial analysts who have a realistic understanding of the necessary requirements. Perhaps the largest field of application lies in geochemical and geobotanical prospecting. I n .;eeking profitable mineralization by the analysis of surface .oil samples or vegetation, metals must be detected
and estimated within a microgram or fraction thereof. It is generally agreed that, although spectrographic analysis is rapid and can detect 5, great variety of elements in one saml:le, in sensitivity i t is inferior by one or two orders of magnitude to the be!jt specific colorimetric methods. I n large scale prospecting, literally mil ions of samples have been analyzed, pirticularly by the Russians (7). Here, the economics of the situation is of psramount importance because the precision required is not too high. .llthough the ‘l‘echnicon Auto ,\nalyzer is not a titrator but a completely automatic colorimetric analyzer, it performs automatic sampling, sequential sample isolation, addition of reagent, any necesswy conditioning, photometry, recording of results, washing or purging of the system, etc.something which few, if any, autotitrators will do. I t has already been applied t o the determination of zinc in soils and sediments (1%)). For many years, the performance of automatic spectrographs, such as the Quantometer, has bemen appraised in terms of man-minutes per determination and cost per determination, as well as the usual criteria of sensitivity and precision. ‘There would seem to be little use for autotitr2,tors that cannot measure up t,o those practical criteria. The importance wliich attaches t o electron probe microanalysis, which combines the techniques of the electron microscope and x-ray spectrochemical analysis, has given rise to a muchneeded treatise on .:he subject ( 1 ) . Birks discusses among other essential topics, the instrumen.:ation in critical detail. Inasmuch as the instrument involves electron opt. cs, conventional microscopy, and the measurement of characteristic x-rays and with the best resources of each, the instrument demands are of the highest order. Stimulating and informative is the chapter on future trends and related uses including low-cost electron probes, the x-ray microscope, electron and x-ray diffraction, and ion-beam instruments. X useful treatise on alternating current polarography and tensamnietry by Breyer and Bauer has appeared ( 3 ) . Apparently the subject was initiated by the author in 1938 ( I S ) , but has been
considerably expanded and augmented by others since that time. The chapter on instrumentation is particularly detailed and complete. Both theory and circuitry are described for a. e. polarographs nith base current suppression, phase sensitive instruments, square wave polarographs, differential a . e. polarography, measurement of harmonics, and specialized instrumentation for such things as the Fournier effect. The practical analyst, not interested in the instrumentation per se, will find a complete description of almost any application to inorganic and organic analysis. ,4n impressive treatise on flame photometry (9), brings the subject up to date as of 1960. All instrumentation, including burners, optics, and electronics, is discussed in great detail and with reference to European and American instruments. I n the introduction, the authors feel constrained to predict that, in a few years, flame photometry as it now exists, will be obsolete-one trend whic.h they note will be the increasing use of atomic absorption spectroscopy. A most useful purpose was served by the publication in this journal, of the symposium on operational amplifiers (2, 4 , 6, 11, 12, 14, 17, 18, 21, 22). For all but the analyst, who long ago threw up his hands a t the hopelessness of mastering electronics, these papers served to bridge the gap between the electronics engineer and the analyst who knows the outstanding problems but is not quite sure of the proper choice of circuitry. The most interesting “Report for Analytical Chemists” by Steele on analytical instrumentation in space exploration (20) lists and describes 18 instruments which are being developed to be used in lunar or planetary probes and to supply information about chemical composition in addition to other mechanical, geological, and biological properties or phenomena. When one considers the enormous difficulties involved, not only in designing the proper transducers, but also the telemetry systems to transmit the information back to Earth and the ingenuity expended in devising entirely original analytical instrumentation, the question arises which qome may share with the author. After we know all about the composition of the Moon,
Mars, and Saturn, will it be indecent or trivial t o inquire if an analJ-sis conducted entirely automatically in Chicago can be telemetered instantly to New York? Or is i t possible to condone this outrageous request if one agrees to let the information be bounced off Telstar relay satellite? Perhaps such things will not come about during this century and we shall have t o content ourselves with building still an other gas chromotograph or polarograph -or an autotitrator. LITERATURE CITED
(1) Birks, L. S., “Electron Probe Micro-
analysis,” Interscience, New York, 1963. (2) Booman, G. L., Holbrook, W. B., AXAL.CHEM.35, 1793 (1963). (3) Breyer, B., Bauer, H. H., “Polarography and Tensammetry,” Interscience, Sew York, 1963. (4) Buck, R. P., Eldridge, R. W., ANAL. CHEY.35, 1829 (1963). ( 5 ) Davies, G . L., “Magnetic Tape Instrumentation,” hlcGraw-Hill, Sew York, 1961. (6) Ewing, G. W., Braydon, T. H.! ANAL. CHEM.35, 1826 (1963). (7) Ginsburg, I. I., translated by Sokoloff, V. P., “Principles of Geochemical Prospecting,” Pergamon Press, Sew York, Oxford, 1961. (8) Headridge, J. B., “Photometric Titrations,” Pergamon Press, New York, Oxford, 1961. (9) Herrmann, R., Alkemade, C. T. J., translated by Gilbert, P. ‘I?., Jr., “Chemical Analysis by Flame Photometry,” Interscience, N . Y., 1963. (10) KeoyJian, E . , Ed., “Microelectronics, McGraw-Hill, Sew York, 1963. (11) Lauer, G., Schlein, H., Osteryoung, R. h., ASAL. CHEM.35, 1789 (1963). (12) XIorrison, C. F., Ibid., 35, 1820 (1963). (13) Muller, R. H., Garman, R. L., Droz, 11. E., ISD. ENG. CHEM.,ANAL. ED. 10, 330 (1938). (14) Murray, R. W., ANAL. CHEM. 35, 1784 (1963). (15) Sews Item, Electronics 37, S o . 8, 17 (1964). (16) Phillips, J. P., “Automatic Titrators,” Academic Press, New York, London, 1959. (17) Schwarz, W. &I., Shain, I., ANAL. CHE!G. 35, li70 (1963). (18) Smith, 11. E., I b i d , 35, 1811 (1963). (19) Stanton, R . McI)onald, A. J., A-Lnal!jst88, 608 (ln6:3).
(20) Steele, P:., ASAL. CHEM.35, X o . 9, 23A (1963). (21) Toren, E. C., I)risroll, C. P., Ibid., 35, IXO!) (1963). (22) Underkofler, W. I,., Shain, I., Ibid., 35, 1778 (1963).
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