Beckmun Award Address
Adve nt u res in Inst ru menta t io n RALPH H. MULLER University o f California, Los Alamos Scientific Laboratory, Los Alamos, N.
I
the Beckman Award in Chemical Instrumentation, a medalist is a t once conscious of the high honor which attaches to the very name of the award. Probably no one is more intimately and completely identified with modern chemical instrumentation than Arnold 0. Beckman. His contributions have ranged from pioneering research, development, design, and organization to public service and sage counsel. It is a source of great satisfaction t o be associated, however indirectly, with this distinguished name. M y contribution to the science of instrumentation has been relatively small but I have had more fun in doing so than any living person. This conviction may explain the title of my address. All research is high adventure. It is the more adventurous and exciting the more nearly it is uncommitted and undefined. This is as true of instrumental research as i t is of research in general. It is increasingly difficult to do pure research in instrumentation, just as i t is in every other field of research. The reason is quite clear. There is so much to be done in modern science and technology that we are prone to use our best resources to get the job done in the quickest and most expeditious manner. All of this leaves too little time to dabble with the new and untried. It is customary, and entirely proper, for a medalist to acknowledge his heavy indebtedness to his former students and associates. I n my case the obligation is particularly pertinent because most of my students were martyrs in an early and slightly disreputable movement. I n the early days of our venture all learned chemists were interested in the Debye-Huckel theory, statistical mechanics, quantum mechanics, and the meticulous determination of activity coefficients and reaction velocity constants. We were “gadgeteers” by commonly accepted terminology, working with such unsanitary devices as phototubes, thyratrons, vacuum tubes, cathode ray oscillographs, and servomechanisms. We were running too near the shoals and the reefs in those days. N ACCEPTING
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ANALYTICAL CHEMISTRY
M.
Anyone will agree that the ringing of a classroom bell is an entirely proper means of terminating even the most learned lecture, but when my first student, the late H. PIf. Partridge, signalled the end point of an automatic photoelectric titration by the ringing of a bell, we really landed in the “raised eyebrows” department. Even after he achieved the more useful goal of automatically shutting off the buret, the hilarity (and disapproval) refused to die down. Things really began to look up when he determined p H colorimetrically with high precision by pliotoelectric means. The scientific world was extremely p H conscious a t that time because careful p H control produced better beer, better cheese, and better pretzels-all highly essential in civilized living. Later, and independently, he turned his attention to vacuum tube voltmeters suitable for measuring the potential of the glass electrode. He was still in the doghouse because the experts were doing pH measurements on the glass electrode in an air-conditioned, electrically shielded room, using the Compton quadrant electrometer. The latter, of course, was hung from a Julius suspension resting on a concrete pier. Does anyone have to be told the rest of the story? How Dr. Beckman, equally confident of the electronic approach, developed the reliable pH meter, a tool now so commonplace that we pay no attention to its “innards” and measure pH quickly and routinely. The students who followed had progressively less trouble and soon their martyrdom reduced to a simple confirmation of faith. I fear that many professors of analytical chemistry are now faced with the converse problem. Probably most of their students insist upon doing analytical instrumentation and abhor conventional analytical research. This would be very unfortunate and I would hope that those who prefer instrumentation are really interested in developing new instruments and not merely in going through the motions. I believe my distinguished students and associates would not want me to go
into a long, historical discussion of their achievements. Old instruments, like old automobiles, belong in a museum, and they would agree with me that, although they investigated wide fields and studied most of these things for their own sake, they Tvere done later by others and in many cases much better. I am sure they would all want me t o recall the guiding light and inspiration provided by the chairman of the Chemistry Department a t New York University-William Caruth MacTavish. This enlightened and genial Scot provided us with handsome equipment. On occasion he couM become a nuisance. I n prosperous times we had to tell him, “Yes Mac, that Hilger double monochromator is indeed a handsome instrument, but we don’t buy expensive instruments-we buy components.” Somehow me managed to match his enthusiasm. There was a time, during this general period, when the department was in a position to offer the whole of analytical chemistry a t the graduate level. Joseph B. Niederl and Anton BenedettiPichler had introduced the quantitative microanalytical techniques of Pregl and Emich into the United States; Alexander 0. Gettler, who was also Chief Toxicologist to the City of Xew York, represented the best in clinical analysis, toxicology, and forensic medicine. In this environment it was impossible for any spectroscopist, polarographer, or electronics gadgeteer to remain oblivious to the larger aspects of analysis. Our discussion of instrumentation should concern the present and the future, but in order that you may know the things which interested us in the past and those people who labored so earnestly on these problems, I have appended a list to this address. I would like to make some general remarks about the science of instrumentation and in particular. about analytical instrumentation. They are personal opinions, based upon long interest in the subject, For those suggestions which have merit, one will say “He is still alert”; for those which are controversial or subject to disproof, he will say “After all, he is getting on in years.”
A friend once remarked, “Muller has an idea every 5 minutes and eben a t 15 cents a bunch they are fun to think about.” I hope t o conduct an economical and retail transaction. A VAST SUBJECT
The many ramifications of instrumentation can hardly be comprehended by a single person. Analytical chemistry is one of the richest fields for its application and there are fem- of its techniques d i i c h are not used, in one way or another, by the analyst. The increasing tendency to develop speciil fields of instrumentation is necessary, but it is unfortunate, nevertheless. We h a r e aeronautical initrumentation, biophysical instrumentation, nuclearreactor instrumentation, and a few dozen other specialties. There are specialties which have somewhat wider application such as electronic3 and servomechanisms. One of our principal problems is to find a means whereby the results and techniques of these specialties can be made more generally available. To a degree such journals as the Review of ScientiJic Instruments, The Journal of
Scientific Instruments, Instruments and .iiitoniation, and the Zeitschraft f u r Instrumentenkunde serve this purpose. Perhaps the only drawback in these journals is that each new technique is described within the context of a particular problem. It is indeed broadening, and a means of improving one’s education in a strange field, to read all of this, but the specific technique which one could use in his own work has to be sifted out of a mass of other inforniation. I shall not yield to the temptation of suggesting a new journal, but if one were ever found to be necessary, I imagine it might bear the title, “Functional Instrumentation.” I n keeping with its title, research reports might state the problem which stimulated the development, but an attempt would be made to emphasize the instrumentation. Depending upon the author’s experience and acquaintance n-ith scientific problems in general, he might indicate other applications. His bibliography would be valuablp to the degree that the ne\v technique would be compared with alternative methods. A t the present time many authors do this very thing, and t o the extent that they indicate other possible applications, they perform a valuable service. The problem is t o find these treasures. They are buried in a hundred different sources.. ROLE OF THE RESEARCH TEAM
These days we seem to be hopelessly committed to the research team in science as well as technology. There
Researches with Former Students
Partridge. TI. \ I . * Wade, I. TI-. Williams, &i.S. Brous, G. C.* Garman, R. L.
Glasor, .I,lr, Spector. .A. Teeters. K.0. Cohen, E. G. Browne, €1. Ii Raker, 11. 11. Burstell,
T.
Ron-land, G. P. McKenna, 11.€1. Droz, 11.E. Greenberg, J. Z. Greenberg, 1,. Reynolds, 11.F. Petras, J. F. t-mberger, W B. Borst, JV. It. Studensl;i, E. Halsex-, ,J. J. Clegg, 1) T,. Vogel, A . LeStrange, It. J. Glickstein, J. Frachtman, H. E. Stolten, H. J. Zenchrlsky, 6 . T.
Automatid photoelectric titrations, photoelectric determination of pH. 1928 Wave length dependence of H-C1 photochemical reaction. 1929 Photoelectric determination of hydroxyacids. 1929 Chemical decomposition by controlled electron bombardment. 1932 >Iwhanism of photochemical reactions sensitized by uranyl ion. 1932 S:dt effects in the absorption spectra of neodymiiim nitrate. 1932. Recording analytical balance. 1935. Oscillographic spectrophotometry. 1936. Oscillographic polarography. 1938 Behavior of substances in a radiofrequencv field. 1034 Fluorescence of manganese-activated calcinm oxide excited by controlled electron bombardment. 1932. A precision radiation integrator for photochemical research. 1934 Studies in fluorescence extinction. 1932. Photometric study of the color change in cobaltous chloride solutions. 1935 Barrier layer cells and the Becquerel effect. 1035 Photoelectric emission as a f:niction of the compwition and sirface character of the emitter. 1931. Study of sensitiaation of cuproiis oxide barrier-layer photocells. 1935 Senpitized fluorescence of boras n-ith rnangancve activator. 1932 Photoelectric photometry of copper. 1032 Barrier-layer cell circuits. 1934. Pulse amplifier for differential electrometric titrations. 1936 Relation between external resistance and poxver devcloped in the barrier-layer cell. 1933. Comparative stitdv of micromethods for the photoelectric deterininntion of copper. 1036. Photoelectric study of the kinetics of manqanese oxidation to permanganate by periodate. 1034. Photometric determination of manganese and chromium. 1936 Photoelectric study of the starch-iodine system. 1936 Oscillographic polarography. 1038. Coulometric analysis. 1938. Photoelectric Dhotometrv of mistiires. 1937 Conductometric stud;. of the system gold bromidepotassium bromide. 1937 Photometrv of barium sulfate suspensions. 1937 Photometric investigation of lead siilfide and copprr srdfide dispersions. 1937. Light ahsorption of riranyl-oxalate systems as a function of pH. 1935 Rapid method for traces of metals by the dropping mercury electrode. 1938. Oscillographic polarography. 1938 S’acuum tube voltmeter for pH and electrometric titrations 1940 Determination of sulfates by photometric and electrometric methods. 1941 Coulometric analysis of iron. 1941 1lethod for the microdetermination cf arsenic. 1948 Paper chromatographr. I. Instruments and technitques. 11. Geometric factors. 111. Kinetic studies. 1951. Instrumental approaches to paper chromatography. 1952 Thermistor compensation for temperature coefficient of condiictance of some electrolytes. 1950. Condiictance instrument for the standardization of analytical reagents 1950 Filter paper disk chromatography. 1052 Automatic integrator for coulometric analysis. 1951 Automatic differential refractometer of high scnsitivity. 1951 Use of thermistors in precise temperature measnrement. 1951. Thermometric determination of micro molecular neights. 1951 Instrliment for automatic determination of melting points. 1952 Research with Associates
St. George, A. V.,and Gettler, -4.0 . h’iederl, ,J. 13. Lingane, J. J. Wise, E. 9. Pllosley, J. R., and Luchesi, C. Lonadier, F.
Radioactive substances in a body five years after death. 1929 Micro potentiometric determination of reducing carbohydrates. 1929 Electronic trigger circuit for automatic potentiometric and photometric titrations. 1948 Use of beta ray densitometry in paper chromatography. 1951 Automatic instrumental methods for determination of critical solution temperatures. Backscattering of beta particles from solutions. 1955. Semiautomatic data plotter. 1956
* Deceased. ~
VOL. 2 9 , NO. 8, AUGUST 1957
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is ample evidence for the success of the team approach. I believe it is equally demonstrable that no team ever discovered a startlingly new phenomenon. This situation applies to instrumentation. If you have a specific effect, well understood and rigorously defined, it is quite possible to instrument the job from beginning to end: for this purpose you call in the team. d chemist, physicist, or biologist sets the parameters, the tolerances, permissible errors, and the effect of environment. I n all probability he will suggest the detector or transducer. The electronics expert now takes over. He does not even hare to know what it is all about. He has a signal to work with and can blow i t up to useful magnitude, I n cooperation with a servo engineer the system can be designed for cancellation of input signal and for the development of power for regulatory function. The computer expert can perform any function in assimilation or computation of the data. To the extent that this corps of experts can do this, we are in the happy state of affairs that almost any phenomenon can be treated in this standardized routine fashion so that we can record, compute, and control. Two questions now arise: How general is this approach, and is it the most economical approach? The answer t o the first is that it is limited only by the phenomenon itself-Le., the extent to which it has some easily measured aspect, and that a suitable transducer exists. The second question is not as easily answered. One drawback of the standardized approach is its formalism. By the very fact that it is bound to work, one is likely to produce something which is very elaborate and costly. In many cases, a careful study of the phenomenon itself will suggest an alternative method and appreciable economies can be achieved. Two pitfalls may be pointed out. Because electronics and computer experts can do almost anything, their blandishments and seduction have to be watched. I say this in complete admiration of their accomplishments but with conviction, nevertheless. The electronics evpert may come up with a 6-foot relay rack with so many tubes in it that forced ventilation is necessary If you are staggered by this a r m \ . he may ell say, “Well, why not do it right?” Similarly, the computer expert mill try to sell you a faultless digital computer and feel slightly sorry for you if you indicate a pieference for a simple analog element. This situation has an easily understood origin There are now many vast projects, most of them heavily subsidized by the Government or the Armed Forces, for which the very best resources are required and in which cost 1 120
ANALYTICAL CHEMISTRY
is a second consideration. This is both the blessing and the curse of modern insewmentation. It is a blessing in the sense that it has led to some fantastic feats of instrumentation. All of these have valuable by-products in the general development of the art. The curse lies in the fact that we are confronted by so many elegant machines for which we could find countless uses but no possible way of justifying their high cost. It is discouraging to the scientist to see an elaborate instrument used 24 hours a day for the performance of routine and monotonous tasks; yet if he has any sense of economic values he can understand why this use is justified and why it would not be justified in satisfying his own curiosity about something fundamental. INSTRUMENTATION FOR ANALYSIS
I believe some general remarks about analytical instrumentation are in order. It does not require omniscience or a crystal ball to see that we are steadily tending toward essential nondestructive methods of analysis. That we have not arrived there by any means is apparent to any component analyst, but the trend is unmistakable. Hence, one may well ask, “What is the probable trend of analytical research?” In many respects, the classical methods of instrumental analysis have been “instrumented” almost to the point of diminishing returns. Perhaps I may be permitted to question the analyst’s curious and continuing addiction tc titrations. If criticism is justified, I must plead guilty before all others, because I have titrated things in almost every conceivable manner-photoelectrically, turbidimetrically by conductance, by refractive index and supersonics, thermometrically, and by nuclear techniques. Fortunately, not all of these mere published. Do we not go to extreme lengths and involve elaborate equipment to perform an essentially IO-cent operation? To the extent that me are committed to titrations and hare to do thousands of them, is not the ideal autotitrator a huge machine which performs every operation, including sampling, a t the rate of hundreds per hour? Conversely, is it particularly startling to watch a recorder draw a titration curve in 10 or 20 minutes with no particularly high degree of precision, and which requires some graphical treatment to locate the end point? I n response to the high and exacting demands of our technology, I believe it may be said that American methods of sampling, testing, analysis, and automatic control are the finest in the world. Our elaborate and expensive equipment is completely justified by demonstrable
savings and improvement in product. But in our supremacy, are we equally cognizant of our obligation to search for fundamentally new things? We have the competence, but do we hale the time? It is revealing and somewhat disconcerting to note our dependence upoii others for fundamentally new techniques and this, despite the fact that we now do them more elegantly thaii many others. Most of our optical and electrochemical methods of analysic had their origin in Iate nineteenth century physics and physical chemistry Among the more recent and widely used techniques, let us look into their origin: polarography and amperometric titrations (Czech), coulometric and electrographic (Hungarian), mass spectrophotometric (British), chromatography (Russian), paper chromatograph) (British), vapor phase chromatograph! (British), tracers (Hungarian), activation analysis (Italian), Aame photometry (Swedish), differential refractometry (Swedish), thermal analysis (Japanese), thermogravimetric analysis (French), quantitative microanalysic (Austrian). It would be foolish to identify these things permanently and completely with the countries of their origin because many nations have contributed to their development and improvement, and instrument mise we have been among the leaders. Then too, scme developments such as microwave absorption. nuclear magnetic resonance, and countercurrent extraction have been essentially American. Can it be that we just have too manj. things to analyze? If so, pyhaps we need bigger and better machines to get these things out of the way and leave us some time for idle curiosity and “unprofitable” tinkering. The most impressive example of seientific curiosity came to my attention when I was a graduate assistant and referee analyst in the analytical department of Columbia University. A graduate student had performed a simple titration. He accidentally bumped the buret stopcock and spilled a few milliliters of reagent on the bench top. Instead of repeating the titration, he proceeded to aspirate the fugitive pool into a weighing bottle and blot the remaining stain with a neat square of filter paper. Some hours later he was carefully titrating the table top, measuring areas, wetting coefficients, and angles of repose. The professor, had he been present, would have thrown him out of the course, but young assistants do not meddle in such sacred rites. My first thought was “May God help his future employer.” But on further reflection, it occurred to me that if he did not forsake chemistry for one of the less exacting professions, such as
law or medicine, and if he did not starve in the interim, this burning curiosity might lead him t o the discovery of something new. I’m sure he is not a practicing analyst. PROPER APPROACH WITH NEW TECHNIQUES
There is hardly a single technique or method which n-e employ which is not worthy of further study and inquiry for its own sake. If we can avoid the urge t o improve and refine it and apply it to some immediate problem, we have the time and opportunity t o learn something new. For example, one of the drawbacks (in my opinion only) of flame photometry is that it works so well! K e control the excitation very carefully, everyone has his own notion about interferences, and yet we manage to get useful and important results. But a luminous flame has many fascinating properties. I t is electrically conducting, is sensitive to electric and magnetic fields and to sound waves. These are worthy of intensive study. Perhaps we should all reread Faraday’s “Story of a Candle” or the early researches of n’ilson and of Arrhenius on flame conduction. Kill these things be productive of new and useful analytical results? Probably not, but who knows? Take the mattcr of thermistors. Their resistance is extremely sensitive to temperature and the chemist knows that practically every chemical phenomenon is temperature dependent. Ergo! Here is a new and better thermometer. Actually this is a gross oversimplification. The tempcrature-resietance function is very complex and the thermistor is not a foolproof thermometer. Beyond this, it has measuring, and compensating and control possibilities, which a t present, are appreciated only by electronics and conimunication engineers. There are countless things which the chemist can do with these, if he can resist the urge to do something immediately useful, such as measuring small temperature differences. There is an urgent need for the derivation of theorems and equivalent net-ivorks employing thermistors, in order to provide a wide variety of temperature correcting functions, Vogel and the author have done this for the temperature coefficient of conductance of some electrolytes. For some five years we were intensely interested in paper chromatography, and a t a time when hundreds of publications were appearing on this subject. As a colleague said, none too complimentary, “Xothing like getting on the band-wagon.” As a matter of fact, we never managed to get on the bandwagon. It bowled us over and ran us down several times. We applied all
sorts of optical, electrical, and nuclear techniques in order to learn just how liquids and solutes migrate through a paper matrix. The studies were completely fascinating and a source of great satisfaction. We well knew that Martin had said most of the things worth saying, and had put this valuable tool a t the disposal of all analysts mho could then continue applying the method without limit. Once more, I believe we contributed less to practical paper chromatography and had more fun in doing so than anyone else. However, I have no doubt that any manufacturer of paper bags knon-s more about the chemistry, physics, and mechanics of paper than all chromatographers put together. Sature has been kind to the chemist; the numbers of chemical compounds which are awaiting separation is legion, so chromatographers have a long and busy future before them. All pure research, if sufficiently illdefined, leads to unexpected results. It turned out from our instrumental kinetic studies that the rate of diffusion of a liquid through paper is uniquely defined by the surface tension, viscosity, and density of the liquid. Furthermore, the temperature coefficient of diffusion is explained by the known effect of temperature on these variables. Another useful by-product of the optical studies led to a simple means of recording refractive index, or variation therefore, of a small quantity of liquid which wets the paper. This is a consequence of light scattering in the cellulose matrix. The presiding officer of this symposium may recall our early preoccupation with such things as oscillographic polarography, oscillographic spectrophotometry, and recording balances. Dr. Garman mas never concerned with ultimate uses. If a new idea appealed to him, his customary question was, “When do we start?’’ I’m sure that as vice president of a large instrument company, he is now required to keep his sights trained on more definite goals, but greater responsibility has not narrowed his vision or his interest in new things. Our second model of an electronic recording analytical balance was developed to a high degree of precision and convenience. Ijothing much came of this a t the time, largely because we failed to explore possible applications. As I recall, only one important application followed our publication. Someone, after conferring with us scaled up the system, and with similar electronic circuity used it to weigh freight cars! Several elegant recording balances have been developed since that time, largely as a consequence of Clement Duval’s stimulating researches in thermogravimetric analysis. It seems to
me that continuing research in the a r t of weighing is needed. No one in his right mind has any idea of greatly improving or supplanting the conventional precision analytical balance. Our famous balance manufacturers have produced superb instruments, and are continuing to do so. There are models of precision and convenience that all but call out the weight in English. Despite this there are innumerable uses for recording and controlling devices of considerably less precision. For some time we have been using the cantilever beam strain-gage type for recording weight a t high speed over a limited load range. Other transducer elements can be used for the same purpose. It is difficult for one to get away from the balance-beam or torsionelement principles, largely for the reason that they are so nearly perfect. Some departures from these principles have been very euccessful, particularly in high-speed industrial application. These are concerned with larger samples than the analyst is interested in, but they can be precise. One thinks of the case in which the single oscillation of an undamped load spring is counted photoelectrically and permits 3000 weighings per hour TTith 0.1% precision. We are currently engaged in some electronic approaches to the measurement of magnetic susceptibility. There are a t least a half dozen schemes which are feasible. The classical Gouy method leaves little to be desired as far as precision is concerned, but it requires a half room full of equipment. Susceptibilities are known for thousands of compounds, but little use of this information is made except in the elucidation of molecular structure The Pauling oxygen gage is an outstanding exception to our rigid dependence upon ancient techniques in this field. Nuclear techniques hold great promise in analytical instrumentation. We are inclined to think immediately of tracer studies, but this technique is so highly developed that little improvement can be foreseen, and it seems to be a matter of unlimited application of known principles. The interaction of nuclear particles and radiation with matter is probably the more promising and unexplored field of research For the past 4 or 5 years our principal concern has been with these aspects of nuclear physics. It is not too appropriate to discuss these here; I have presented them before the Industrial and Engineering Division. CURRENT NEEDS
Despite the breath-taking pace of instrumental development and its generally accepted accomplishments, there seems to be a continuing necessity to VOL. 2 9 , NO. 8, AUGUST 1957
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explain its needs and its implications. To my mind, the most urgent problems are those of research in instrumentation and the training of instrument specialists At present these are accidents of employment or a matter of individual interest. Before we can tackle these difficulties we require some definitions; even such a simple matter is difficult. There seems to be more difficulty in this among chemists than in any other group. I believe we can ill afford to sit back and say that an analyst should be trained in fundamentals and should learn the additional gadgetry in onthe-job training. This a t once raises the question, “1t7hat is fundamental?” I s it the nature of precipitate formation, the calculation of solubility products, or redov potentials? The analyst mho uses the mass spectrometer, the infrared sl~ectropliotorneter, vapor phase chromatography, or x-ray diffraction may know these things, but there are other things far more important to him. This reminds me of the early arguments about chemical engineering. Sometime around World War I, sonieone proposed a new curriculum to be called Chemical Engineering. A prominent dean of that type snorted “Oh. . ., give them a sound course in chemistry and sin IT-eeks’ training in pipe fitting.” Is there any one today who is willing to descrilx the profession in those terms, or who doubts the indispensable function of tlip chemical engineer? I believe it is too late to make any effective compromise between analytical chemistry and instrumentation; both are vast subjects in themselves. One might hope that analysis could be taught in its entirety-not just gravimetry and titrimetry, and exclusively inorganic at that! With no referencr to instrumentation gadgetry or push buttons, a redefinition of fundamentals of analysis is in order. If such alleged emphasis on fuudanient:ilj ignores distillation, chromatography, elementary organic analysis, functional groups. and dozens of other important topics, it misses the point and the futurg of analysis will pass into the hands of the physicist-who rarely knows any chemistry. I t is high time for a unified offering in instrumental science. A distinguished thermodynamicist once defined physical chemistry for me. “It’s all very simple,” said he. “To be a physical chemist, you merely have to be a chemist, physicist, mathematician, carpenter, plumber, tinsmith, and glass blower. If, in addition, you can teach, it will help you to understand rvhat you are doing.” The same can be said of modern instrumentation with a few extra techniques thrown in. About 10 years ago I proposed the es1122
ANALYTICAL CHEMISTRY
tablishment of a n Institute for Instrument Research which would foster fundamental research in all phases of instrumentation and, in collaboration with a sponsoring college or university, would offer instruction in the science of instrumentation a t all degree levels. I reproduce the organizational chart here. It would need revision in several respects. This plan \vas reprinted at that time in Instruments. A nationwide inquiry elicited replies about the same as the aforementioned dean’s; less profane, but equally enthusiastic. These things take time. As any profeesor knows, it takes 15 years to get a single new course into the curriculum and a t least 20 years to get it out of the curriculum after it has outlived its usefulness There are faint but encouraging
signs. The Instrument Society of America is contemplating something of this sort, and if there are enough peoplt. who are net too busy on the production line, something may be accomplished. No discussion of instrumentation. however brief, could afford to neglect the magnificent role played by our instrument companies. Kot only do they provide us with countless components and devices for research as well as elegant instruments for almost every conceivable use, but they also provide an impressive amount of fundamental information on theory, application, and uses of their instruments Practically all of the larger companies maintain a number of research and development engineers dedicated to thv improvement of instruments. Despitr.
ASSOC. DIRECTOR Organization, Personnel, Technical Instruction
BUSINESS MANAGER Finance, Industrial Fellowships, Contracts, Patents
DIVISION HEADS
THEORY Theory of Instrumentation, Principles of Automatic Control; Computational Devices
ANALYTICAL CHEMISTRY Instrumental and Automatic Methods of Analysis and Control
PHYSICS Physical Measurements, Optics, Heat, Sound, Properties of Materials
I
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CHEMICAL ENGINEERING Plant Processes and Control
BIOLOGY Biophysics, Biochemistry and Medicine. Instrumental Problems
DOCUMENTATION Library, Data, Reports, Technical Photography
ELECTRONICS Circuit Theory and Design for Measurement and Control
SERVOMECHANISMS Instrument and Control Servos
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I N S T R U M E N T SHOP Construction of Experimental Systems and Models
ENGINEER I N G Instrunlent Design and Mechanism
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their competence and broad vision, I believe we would be unfair to these companies to expect them to carry the full burden of research in instrumentation. They must continue to depend upon fundamental research done elsewhere. Given a new and promising principle, they can be relied upon to develop and improve it and reduce it to eminently practical form better than most of us. One might hope to see more of the thing represented by the Office of Basic Instrumentation a t the National Bureau of Standards, under the able direction of Mr. Wildhack. I f I may summarize these random
observations, I would say that we can describe the status of present-day instrumentation and some of its needs as follows: There exists a unified and more or less general approach t o the instrumentation of any phenomenon. This includes detection, measurement, recording, control, and data assimilation. There is need for more pure, uncommitted research in rare and obscure phenomena. The trivial or obscure effect of today will be the industrial practice of tomorrow if history is any guide. The need for training instrument scientists a t all degree levels must be met if we are to avoid the tangential
trend toward specialization which already exists. Instrumentation is largely responsible for our technological supremacy. In that category no amount of expense or elaboration is excessive because it ultimately pays for itself. To the extent that these costly things can be justified in pure research, they afford us insight, in almost infinite detail, into the most complex phenomena. To an increasing degree, the amount of information which we can obtain on any problem is limited only by the resources which we can afford t o apply to them. Despite thi!, all evidence indicates that the best 1s yet to come. For the curious, the venturesome, and the visionaries there shall continue to be high Adventures in Instrumentation.
General Procedure for Setting Up Infrared DifferentiaI Analyses of Multicomponent Mixtures JOHN A. PERRY and GEORGE H. BAIN' Research Deparfmenf, Sfandard Oil Co., (Indiana), Whiting, Ind.
b Differential spectrophotometry can greatly improve the precision of infrared analyses of multicomponent mixtures. Wire screens make convenient references against which samples can b e matched in differential measurements of absorbance. A sequence of steps is proposed for straightforward calibration for differential analyses of multicomponent mixtures. The steps, including data handling, are illustrated in detail b y reference to an analysis of a six-component Cd hydrocarbon gas.
P
almost always limits the precision of infrared analyses of multicomponent mixtures. The response of infrared detectors is linear with transmittance, but logarithmic with absorbance, which is proportional to the concentration of the infraredabsorbing components. The constant error in measurement of transmittance corresponds to an absorbance error which increases with absorbance. Thus, the higher the measured absorbance, the higher the absolute error in measurement of concentration. This relationship seems to impose a ceiling on the precisioii of photometric determinations. Differential spectrophotometry (4) raises the ceiling. I n this technique, HOTOMETRY
Present address, Whirlpool-Seeger Corp., St. Joseph, Mich.
:I sample is precisely matched against a standard, permitting absorbance to be measured within about 0.002 unit over a wide range. Making standards which nearly match the samples in coniposition is time consuming and expensive (1, 5 ) . Only the absorbance of the sample must he matched, not the snniple itself. Wire screens, properly used. are good standards of absorbance. Calibration for differential analyses of multicomponent mixtures is inherently more complicated than for conventional, hon-ever. It can be simplified by following a definite suitable sequence of steps. Such a sequence. applicable to gas or liquid saniples, and making use of wire screens, has been devised. In this procedure, screens, the ratio method ( I O ) , and auxiliary curves are nsed. The screens serve as standards of absorbance. The ratio method is characterized by its determination of :tbsorptivities, handling of matrices from these absorptivities, and reliance on mixtures of known composition. Complementing the ratio method by nuxiliary curves eliminates systematic errors from results.
EQUIPMENT
Photometric measurements are to be made on an infrared spectrophotometer. Wave length calibration of any infrared spectrometer, thermostated or not,, should be checked within 2 hours of
any reference measurement, and suitable corrections applied. Wire screens, such as sections of 16mesh wire gauze, are suitable reference absorbers for a single-beam PerkinElmer Model 112 spectrophotometer, which is well suited to this procedure. Such an instrument carries shutter holders in which wire screens can be mounted and which protect the inherently rugged screens from injury and dirt, so the screen absorbance does not change with time. Combinations of screens can be used to cover a wide absorbance range. Each screen is so oriented that the wires line up neither with the slits of the monochromator nor with wires of other screens. Becausty the light beam is wide a t the shutter, the absorbance of each screen is independent of sniall lateral changes in position. The screen, to be inserted in a narrow light beam, as in a Beckman IR-2, must h a w a fine mesh to preserve a low (screen wire diameter to beam width) ratio. Such a screen can he mounted in a cell holder and carefully protected when not in use. PROCEDURE
The steps in setting up a differentixl analysis are: specification of instrumental conditions, measurement of reference materials, and calculationb. The specific procedure evolved is applicable to samples having stated components falling in their stated concentration ranges. Instrumental Conditions. Selection of wave length, choice of signal level, VOL. 2 9 , NO. 8, AUGUST 1957
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