The Teaching of Chemical Instrumentation - Analytical Chemistry

Report Galen W. Εwing a Benedict Visiting Distinguished Professor Carleton College Northfield, Minn.

Maarten van Swaay Professor of Computer Science Kansas State University Manhattan, Kan.

The subject of instrumentation is of such importance in modern chemistry that teaching about it on both the un dergraduate and graduate levels is es sential to all disciplines in which chemistry plays a part. This REPORT explores some of the questions and di lemmas facing those who teach the subject and those who establish un dergraduate curricula in chemistry. Separate courses in instrumental analysis, as they were developed soon after World War II, generally paid scant attention to the basic chemistry of analytical procedures. Often only a few commercial instruments, such as pH meters and photoelectric photom eters, were available for student use, and much time was spent on the de sign of home-built apparatus. Other types of instruments, such as spectro graphs and polarographs, could be treated only as library research projects. There seemed to be no way to integrate this material with classi cal analysis. Over the years, as more and more instruments were developed, it be 0003-2700/85/0357-385 A$01.50/0 © 1985 American Chemical Society

came less realistic to maintain artifi cial barriers between "instrumental" and "noninstrumental" analysis. Nev ertheless, this dichotomy has been perpetuated in many institutions for reasons of expediency. One factor with far-reaching ramifi cations has been the extensive treat ment of certain instrumental tech niques in college courses that are not labeled as "analytical." This trend originated long ago with the study of spectroscopic methods in connection with the elucidation of atomic and molecular structure, as presented in the physical chemistry course. It has been accentuated by the reliance of organic chemists on data from absorp tion spectroscopy, NMR, and mass spectrometry. Thus it has become convenient for curriculum planners to assume that all the necessary informa tion about these important techniques is adequately covered in other courses. At first glance, this would seem to be an efficient and satisfactory ar rangement, wherein each technique is taught by those most interested in its

application. The danger is, however, that students will be led to take for granted the internal operation of in struments, without adequate appre ciation of their limitations. Addition ally, the instructor in organic chemis try may have neither the time nor the interest in the theory of instrumenta tion to enter into a detailed examina tion of alternative instrument designs. It seems clear to us that instrumental analysis should always be taught by an analytical chemist. In some institutions an attempt has been made to integrate instrumental and classical analytical techniques into a single course, typically under a title such as "Quantitative Chemis try." The presentation can then be problem oriented, making use of any appropriate techniques, whether clas sical or instrumental. This has the great advantage of more closely dupli cating real-life situations that an ana lytical chemist is likely to encounter, in which he or she must select as well as implement the method to be used to solve a problem most effectively. However, this may result in a course that is too long to fit readily into the curriculum. Hence in many schools two separate courses persist. The instrumental seg ment invariably comes later in the student's program than the conven tional "quant" course, thus taking ad vantage of greater preparation in physics and physical chemistry. This course may or may not be required of chemistry majors and is seldom taken by biology or premedical students. ° Present address: P.O. Box 2573, Las Vegas, N.M. 87701

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985 · 385 A

The instrumental analysis course

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Let us assume, then, that the instrumental aspects of analytical chemistry will be taught in a separate course. What should be included and what omitted? The necessary compromise between breadth and depth presents a knotty problem. Should we be satisfied with a relatively superficial treatment of many types of instrumentation, or would it be preferable to select a few areas and explore them more fully? One possibility that may be attractive to the professor is to treat in considerable detail one or two subjects with which he or she feels most at home. The hope then is that the general method of approach developed here can readily be adapted to other disciplines. This may, however, give the student a distorted view of the relative importance of various techniques. No matter what approach is adopted, there must be a decision as to the

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degree of mathematical and physical detail to be introduced. Should all equations be rigorously derived, or should those of lesser pertinence be taken on faith, with references given to more complete coverage in the literature? For example, Fick's laws of diffusion as applied to polarography can easily be used without theoretical background, but a rigorous derivation of the Ilkovic equation is essential. Few chemistry teachers would attempt to explain in detail the algorithm for the fast Fourier transform or the detailed theory of the Michelson interferometer as necessary background for a discussion of FT-IR. The real question is where to draw the line, and this is a decision that must be left to the professor. He or she will, no doubt, take into account the available textbooks, and there is quite a variety from which to choose. The professor may prefer a text that includes in an encyclopedic manner a great deal of factual and theoretical material, including the derivation of all significant mathematical relations .from first principles. Such a text can hardly be covered in toto in a one- or even two-semester course, so that the instructor must specify which chapters or portions of chapters will be included. On the other hand, it is possible to choose a text that presents the framework on which the instructor can hang as much or as little detail as seems desirable, often amplifying the textual material in his or her own field of expertise. The treatment of each type of instrument should stress the flow of information from the chemical domain, via a transducer and suitable electronics and data processing, to a final report in a form that is directly meaningful to the ultimate user. The limitations of each instrument should be presented in a format that permits easy intercomparisons of parameters such as signal-to-noise ratio, sensitivity, achievable limits of detection, and speed of measurement. The laboratory

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386 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985

Curriculum planners must decide whether or not to include laboratory sessions specifically tied to instrumentation. Some top-rated institutions do not, relying on a generalized "Advanced Lab" course to include sufficient experience with instruments. If a separate laboratory for instrumental analysis is decided on, a question arises regarding the desirable degree of involvement of the student in the design of instruments as contrasted with their use only. If only commercial instruments are used, experiments must be specifically designed to acquaint the student with

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the many available modes of operation. A difficulty often encountered with this latter approach is the unavailability of state-of-the-art instruments in purely educational laboratories. In many institutions expensive items are necessarily purchased on research grants and can be used only by participants in the designated research programs. Instruments for teaching laboratories are likely to be old models, donated to the school by local industries that see a chance to combine academic goodwill with a sizable tax writeoff. In this respect some small undergraduate colleges may be better off than their large university neighbors; there is a closeness between students and research projects in the smaller institutions that makes modern instruments available to all if they are present anywhere in the department. Lacking such instruments, the instructor should consider the use of computer simulation—programming a computer to produce data that appear to have come from an analytical instrument.



On the other hand, a modular approach can be adopted. The student is asked to synthesize working instruments from available parts, such as light sources, monochromators, and detectors, together with a large selection of electronic building blocks and measuring gear. It is obviously impossible to train a student to be a competent mechanic, an up-to-date electronics wizard, an expert in optics, and a polished computer programmer, as well as a good chemist. The ideal is a noble one, but the practice must be more realistic. A good instrumentation curriculum should provide students with enough understanding of the fields of electronics, mechanics, optics, and computer science to allow them to cooperate effectively with experts in those fields. It is unlikely that a computer scientist will spend the time to learn the details of, for example, NMR, or that an electrical engineer will be familiar with the nonlinear behavior of the impedance of an electrode surface. In contrast, the chemist is invariably confronted with equipment that relies heavily on state-of-the-art electronics, mechanics, and optics. It is therefore incumbent upon chemists to learn enough of the technical fields that they can at least make their wishes known and be able to evaluate with reasonable confidence the tools constructed by their technical friends—to be sure that such tools will fill the requirements of their chemical problems. Electronics Over the past 10 years electronics has progressed to the point where the transfer functions of standard and easily used building blocks can be represented by simple mathematical expressions with an accuracy that meets or exceeds that of most of the sensors found in the laboratory. A good grasp of mathematics will then go a long way toward the implementation of many useful pieces of equipment. Similarly, standard digital function blocks allow the construction of impressive pieces of dedicated logic with only modest understanding of the circuitry inside the individual units. The convenience of standard electronic building blocks has allowed chemistry students to achieve a useful degree of proficiency in their use in a very short time. This apparent success, however, comes at the expense of instilling a false sense of competency. A semester of electronics dealing with potentiostats, integrators, temperature controllers, and digital timers is by no means comparable to a curriculum in electrical engineering. The goal of the electronics exposure thus must

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be twofold: The student should be convinced that much useful equip ment can be created with a very mod est amount of circuit design but must also recognize that such results are possible only because the performance of the building blocks available usual ly far exceeds a student's needs. The design of equipment that approaches the limit of electronic performance will always require competence far be yond what can be offered in a chemis try curriculum. Computer use The place of computers in the chemistry environment has changed just as spectacularly as that of elec tronics, but with entirely different consequences. In contrast with most other equipment, computers can accu mulate a mass of recorded data for fu ture digestion. Consequently, comput er applications tend to be used not only by the designer and programmer, but also by his or her teammates and successors. This dictates rigid disci pline in areas such as program struc ture and style, data representation, and documentation. Only a few years ago, the primary use of computers in the chemistry lab oratory was for data acquisition. Oper ating systems would support only a limited set of operations, including storage of data on tape or disks. In spection and processing of data were almost invariably done in a separate step (off-line) to avoid real-time com plications. Consequently the data ac quisition could be kept very simple, and any processing of data was effec tively shielded from the laboratory en vironment. The demands on pro gramming skill were correspondingly

The cost of computers has gone down, their perform ance has improved, and the ambitions of the chemists using them have grown.



modest, and most students could create programs that satisfied the needs of their own research or course work. Quite often, however, such pro grams could only be called disposable: They might be useful to the designer, but they could not be maintained and would invariably contain quirks that precluded their use by others. Recently, however, the cost of com puters has gone down, their perfor mance has improved, and the ambi tions of the chemists using them have grown correspondingly. Chemists are no longer satisfied with mere data logging; they wish to control their ex periments on the basis of the current data stream. In addition, the conve nience of data collection has resulted in rapid accumulation of large files of data that can be managed only with the help of computer search tools and other data-handling techniques. These higher ambitions are directly reflected in program complexity, which in turn requires expanded program invest ment. As a result of these developments, chemists now realize that proper pro gramming style and documentation habits are no longer mere buzzwords used by computer scientists, but are becoming a necessary discipline for the chemist who uses a computer. Here again, teachers of instrumenta tion in chemistry must strike a bal ance. They can introduce enough ma terial in one semester to allow stu dents to create small programs that will meet their immediate needs, but they cannot hope to train program mers or computer scientists in that time. Unless students are warned ex plicitly, their success in making a com puter obey them may give them an in flated sense of their ability. It is only too easy to find lab drawers full of disks and tapes with undecipherable data that were collected without re gard for program discipline. There can be no doubt that expo sure to computers has a place in the chemistry curriculum. It is also true that those aspects that are specific to the laboratory environment (analogto-digital conversion, experiment syn chronization, data representation as x-y plots, and so on) cannot readily be treated in service courses offered by computer science or engineering de partments. The limited amount of time available for computers in the chemistry curriculum must be re served for information that students cannot obtain elsewhere. These might include discussions about interfaces to instruments available in the depart ment and exposure to application soft ware packages that have been devel oped for such use. The task of instilling good habits of program style and documentation is

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Galen Ewing (right) received his for mal schooling at the College of Wil liam and Mary and the University of Chicago. His industrial experience in cludes work at the Sterling- Winthrop Research Institute and at Central Scientific Company. His chief inter est, however, has been in education. He has taught at Blackburn and Union Colleges and at New Mexico Highlands and Seton Hall Universi ties. Now retired, he continues writ ing textbooks in analytical instru mentation and electronics. Maarten van Swaay received his edu cation in the Netherlands and at Princeton University. In 1963, he joined the faculty of Kansas State University as an analytical chemist. Over the years, he became progres sively more interested in instrumen tation and then in computer applica tions. For the past three years, he has been a full-time member of the De partment of Computer Science at Kansas State, still maintaining ties with his former colleagues in chem istry.

The Teaching of Chemical Instrumentation - Analytical Chemistry

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