some ideas on analytical chemistry courses for chemistry majors
TRANSCRIPT
Some Ideas on Chemistry
Courses for Chemistry Majors
ROLAND F. HIRSCH Chemistry Department, Seton Hall University, South Orange, N. J. 07079
MΥ TOPIC is a general one: analytical chemistry as part of the
education of chemists. This topic is of interest today, beyond the normal réévaluation and revision that should occur in the teaching of any discipline, because some chemists are questioning whether analysis has any place in academic chemistry and many others sec only a minor role for it in comparison with the past.
I must admit that I have somewhat limited experience in the teaching of analytical chemistry. In my five years at Seton Hall I have had the opportunity to teach both graduate and undergraduate courses in analytical chemistry. I have taught the basic courses taken by all chemistry majors at both levels and have been able to make changes in these courses and observe the results.
I have concluded that analytical chemistry as presently taught, and as presented in its textbooks, does not reflect the true state or nature of the field. My discussion today will try to focus on the essential aspects of analytical chemistry, for I believe it does have a contribution to chemical education if its real principles are considered.
To present my conclusions, this paper has been organized into three parts: first, the reasons for the current low standing of analytical
chemistry in academic circles, in terms of the wrong premises which we as analytical chemists have adopted as the bases for our courses; secondly, my views of what the fundamental objectives of analytical chemistry courses should be, and, finally, the outline of a basic course in modern analytical principles. These remarks are intended to refer to a junior/senior level undergraduate course for chemistry majors, but there will be implications for the basic graduate-level course as well. I t is not my intention to infer anything about the specialized courses iii analytical chemistry.
I must also admit that what I have to say does not give a balanced picture of the situation. Each viewpoint has its supporters, and though I may not give the others their due because of limitations of time, I can conceive of valid reasons for disagreeing with what I have to say.
What is Wrong?
It is, first of all, a matter of definitions. We can define analytical chemistry as the study of materials to determine their composition, usually in chemical, occasionally in physical, terms. What then does one teach as "analytical chemistry?" Well, analytical chemists do certain things in their work.
They use certain principles in designing their methodologies. These principles are built on the basic laws and theories Of chemistry and related fields. It is my belief that in analytical chemistry courses, too much emphasis is placed on
—what analytical chemists do —a specific methodology, namely
interpretation of spectra —those principles which can be
presented in a rigorous manner
Let me now explain my objections to each of these in turn.
Why shouldn't analytical chemistry courses for all chemistry students emphasize "what analytical chemists do?" Why isn't it appropriate to devote most of the available lecture time to describing the techniques and methods of our field, and why isn't it sufficient to use the laboratory to train the students in the skills we use as analytical chemists today?
Well, perhaps the most important objection, as far as I am concerned, is that this is not teaching the future in which our students will be working, but rather the past and present. Looking back 20 years, just half a professional lifetime ago, can we say that what analytical chemists did then corresponds to what they are doing today? To be sure, some training for the immedi-
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ate future is necessary, but remember that we are not training the future analytical chemists alone, but all types of chemists.
The second objection I have is that what analytical chemists do represents an almost bewildering variety of methods and techniques applied to a tremendous range of types of samples. There isn't enough time in a college course to cover all aspects of methodology and applications or even a significant fraction of them. Furthermore, the methods shouldn't be learned as such anyway, for most of them will be quickly forgotten and can be easily looked up if necessary.
This is not to say that "what analytical chemists do" should be excluded from the basic analytical chemistry courses. Techniques will be covered to some extent, especially in the laboratory. Methods and applications should be used throughout the course as examples, carefully chosen to illustrate principles. Also, the students should be thoroughly acquainted with the sources of reliable methods, such as the ASTM, APHA, the Treatise on Analytical Chemistry, and the important journals.
Lately, courses dealing primarily in the interpretation of the spectra of organic compounds have become popular. Many institutions offer courses of this type in conjunction with organic and biochemistry courses, usually at the sophomore level. There is nothing wrong with this type of course—provided it does not represent the main or the only exposure of the chemistry major to analytical chemistry. I t is my feeling that this kind of course is going to serve as an excuse for eliminating the independent analytical chemistry course from those required of all chemistry majors at many institutions.
The fact is that the interpretation of spectra type of course misses many key principles of analytical chemistry. I t is presented early in the curriculum and has a very limited goal—to teach students how to use an admittedly valuable tool. Being tied to the organic chemistry course, it cannot include a balanced presentation of analytical chem
istry, even if a few chapters and experiments on titrations and chromatography are thrown in.
Another danger I see is that the interpretation of spectra of organic compounds is something that many nonanalytical chemists can do better than most analytical chemists, because it is a tool that they as organic or inorganic chemists make use of constantly regardless of what their specialty may be. To teach interpretation of spectra best, at most colleges and universities, it therefore should not be the responsibility of an analytical chemist, but rather of someone else who probably isn't that familiar with current thinking in analytical chemistry. Therefore, if it is conceded that this kind of course is all that every chemistry student need see of analytical chemistry, then the other types of chemists will get the impression that the real anaytical chemist is superfluous since they can teach this better than he can.
This is, I feel, a real danger. Academic chemists in general may lose sight of what of analytical chemistry is really fundamental to all chemistry. There must be a distinctive purpose to academic analytical chemistry if it is to fluorish —indeed, to survive—in colleges and universities.
The analytical chemistry course based on a rigorous development of a limited number of principles is a tradition carried over, in my view, from the earliest days of quantitative chemistry, when close attention to exactness was necessary for advances to occur in the science. At one time the weight and volume relationships were the only important chemical laws or generalizations, and they were therefore the most essential part of a chemist's training.
Looking at the currently available analytical chemistry texts, I believe that a disproportionately large amount of space is devoted to gravimetric and volumetric analyses, usually with but a few chapters on other aspects of the subject added on toward the end of the book. Now I will agree that the pedagogic value of precision drill in
lecture and laboratory is undeniable, but is it time well spent, considered in light of the overall nature of analytical chemistry? Is it healthy for our discipline to offer upperclass, sophisticated chemistry majors, a whole semester consisting of a mixture of principles and ideas which were developed at least 30 years ago, as being the most significant ideas they can learn from us for their future work?
The fact is that many if not most analytical problems today are, and tomorrow will be, of a low-precision, ball-park answer, rather than a high-precision type. In clinical analysis, for instance, it is not a question of finding to the nearest tenth of a percent relative the glucose or calcium or albumin content of a patient's blood, not even to the nearest 1%.
Furthermore, many of the most useful analytical principles resist precise quantitation. Even acid-base equilibrium calculations are meaningless beyond two significant figures (maybe even only one significant figure is justified) in practical cases because of activity effects. Putting it another way, we don't have enough control over our environment—τ-the analytical system—to calculate very many useful things with good precision.
Therefore, let's not emphasize precise calculations and methods (volumetric and gravimetric) in our courses. The students will be introduced to these concepts in the general chemistry course, where they are naturally a part of the development of atomic and molecular theory. The details of the advanced calculations and methods can be found in reference books and handbooks. The results, say of a complex pH calculation, are best found anyway by experimental measurement, such as by using a pH meter.
What Should Be Done?
Having described what I feel is wrong with the teaching of analytical chemistry today, I would like now to offer a prescription for restoring the vitality of our field as an academic subject. First I will discuss my list of the most impor-
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tant principles of analytical chemistry; then I will present an outline for a course which covers them.
I believe that each of the ideas to be enumerated is essential in the education of a chemist—any kind of chemist. I t is my view, furthermore, that each of these ideas is best presented in the context of the analytical chemistry course. In other words, it is through .these ideas and concepts that I believe we as analytical chemists can have an essential role in chemical education.
I jet me carry this point a little further. Organic and inorganic and biochemists are limited in the types of chemicals and reactions they have to treat and by the theories that are popular today and hence "must be covered." Physical chemists today emphasize the mathematical formalisms so that they can keep up with what their peers are doing. General chemistry courses, if they are general, are taught at a point at which most students have limited knowledge of chemistry.
I believe that the analytical chemist has an opportunity not open to the teachers of the other courses in chemistry. I t is an opportunity to be a generalist, to get to the heart of things chemical, unencumbered by any of the burdens just alloted, perhaps unfairly, to the others.
I recently came across an article that impressed me very much in this regard. I t is called "Strong Inference," by J. R. Piatt, and it appeared in Science ill 1964 (1). Every chemist, surely every analytical chemist, should read and ponder what Piatt has to say about the kind of reasoning which leads quickly to important conclusions through the choice of the key experiments. We can teach our subject in a way that will encourage sound reasoning and intuition, rather than the learning of the formalisms, details, theories, and mathematics which are unnecessary to understanding.
Fundamentals of Analytical Chemistry
The first fundamental of analytical chemistry I will call the concept of a signal. There are two types of
signals, analog and digital, and we should develop an understanding of the characteristics of each. Here I might note that there is some confusion between the nature of the signal and of the readout, as is evidenced by the appearence of so-called digital pH meters. In analysis, the signal must be defined in relation to two other factors, the background and the noise, and here also I feel that the distinction is not always made clear in analytical courses. The concept of limit of detection is also part of the idea of a signal.
Closely allied with these concepts are the ideas of accuracy and precision, particularly the statistical basis for handling experimental data. In this regard, I think it is unfortunate that less than half of the currently available analytical texts distinguish between the standard deviation of a method (that is, of a single result) and the standard deviation of the mean, even though most books do define confidence limits, usually as t • s/~vn, rather than t • sm. The square root law sm = s / V n is such an important concept in discussing precision of analyses that it should be brought out in analytical chemistry courses right from the start. By the way, it has been said that the number of good scientists is also proportional to the square root of the total number of scientists (β). An important point regarding precision is that something is wrong if the experimental precision is much better than that predicted by propagation of errors, as well as the more obvious fault in the reverse case. The use of statistical tools as aids to common sense should be stressed in the analytical course.
The second fundamental principle of analytical chemistry is that of experimental design. I t is true that this is implicit in the discussion of organic synthesis, for example, but the analytical chemistry course is the place where it is developed best in more general terms. There are two aspects to experimental design we should cover. First there is the strategy of research and method development, a
kind of overall design to original work. This can be taught with reference to the many instructive anecdotes in the book by Beveridge, "The Art of Scientific Investigation" (3), which avoids a dry recitation of the stages of the so-called scientific method. A more specific example that I use in discussing experiment design is the Simplex method of optimization of conditions. The article on this topic by Long (4) is very helpful.
The other kind of experiment design we need to concern ourselves with might better be called method design. Here I refer to the tactics that are employed to be sure that a procedure will actually work when applied to real samples. One should discuss the various types of standardization and pei'haps also the use of control charts to check for faulty behavior of a method.
The third group of fundamental concepts of analytical chemistry comes under the heading of instrument design. Here the discussion should center on the electronic, optical, and mechanical components and operations which can be used to (a) generate a result, and (b) extract this information from the accompanying noise.
Some understanding of electronic circuitry and optics is necessary, but I believe a modular approach to instrumentation should be used as much as possible (o). Operational amplifiers, for example, can bo discussed in this fashion. The techniques of signal-to-noise ratio enhancement, such as modulation and time-averaging, should be developed as concepts (6).
]\Text on my list are the principles of the phenomena of nature which can bo quantified and hence which can be used for analysis. Any property which is descriptive of a chemical system—which aids in specifying a particular system—is appropriately discussed in the analytical course. The treatment should be qualitative for the most part, with a minimum amount of theory and derivations. The emphasis should be on an understanding of what is going on and how it might be useful in analysis—in
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other words, a practical approach. The theoretical aspect should in the main be presented in the form of useful generalizations such as the Nernst and van Deemter equations —namely, the theories that really work. Frank (7) recently noted with regard to the structure of water, "after many years of speculating about what water 'might he like in order that it display certain properties, we can now begin to ask what water must be like if certain pieces of data are . . . reliable." We in analytical chemistry should be sure that we are teaching the latter type of theory or model.
I particularly emphasize the conditional conception of equilibria as developed by Ringbom (8). From the point of view of analytical methods, the idea of side reaction coefficients is a most important concept. All kinds of equilibria can be presented using this approach. The arithmetical similarities among the different equilibrium systems, homogeneous and heterogeneous, can be brought out in this way, avoiding misunderstandings and allowing more time to be spent on the actual chemistry.
I place the ideas of stoichiometry and quantitative relationships last on my list of fundamentals of analytical chemistry not because they are least important, but for the reasons discussed earlier: They are already introduced in general chemistry courses and they have been overworked in analytical courses.
Before presenting the outline of a course which tries to follow these "guidelines," I would like to make one final generalization. I think it very important that the analytical course emphasize the interrelationships and similarities between various phenomena. I just mentioned this as an approach to discussing equilibria; let me now give a few other examples of how this can be done. One good case is that of the steady state. This principle appears over and over in the analytical course, such as in discussing secular, transient, and activation equilibria in nuclear chemistry, chain reactions involving enzymes
and other catalysts, precipitation from homogeneous solution, and stopped-flow measurements. If a student can understand the kinetics in one of these cases he will have much less trouble understanding the others if the conceptual similarities are pointed out to him. Likewise the electrical plasmas involved in arc and spark spectroscopy, radioisotope decay detectors, and several gas chromatography detectors are based on similar phenomena. The fact that diffusion coefficients increase with temperature has an effect—not the same always—on both line widths in atomic spectroscopy and peak widths in chromatography.
A Course Outline for Analytical Chemistry
My course assumes that the students are juniors or seniors, with a good general chemistry course and some background in organic chemistry, but no additional physical or inorganic chemistry is necessary as preparation. Probably it would require two semesters to cover all this material. A single semester would be sufficient if the main goal were to introduce the students to the subject of analytical chemistry with the expectation that they will later go out and learn on their own whatever details they need to know in their work.
The first section of the course is devoted to the general features of experimentation—types of errors, statistical tools, experiment design, standardization, presentation of results in the form of tables, graphs and equations, and sampling. There would follow a review of quantitative concepts, volumetric calculations, and equilibria, if necessary.
The second section of the course is devoted to equilibrium principles. Perhaps this should come later in the course, after a discussion of instrumentation, but the laboratory starts out with wet chemistry and separations so equilibria come early in the lectures. I emphasize again the importance of applying the conditional equilibrium constant approach to all types of equilibria. Solutions are discussed
first, with a section on titrations in which the elements of instrumental techniques are brought in in connection with the development of end-point detection methods. EDTA titrations are discussed in some detail because of their practical utility, as well as Karl Fischer titrations and other types of iodim-etry, and functional group analysis by titration. I admit to a somewhat personal choice of examples here.
Nonaqueous and molten salt equilibria come next, followed by all types of heterogeneous equilibria. Next I treat flame and electrical plasma equilibria, with frequent mention of applications of the principles to problems in spectrometry. Finally, nuclear reactions are discussed from the thermodynamic viewpoint. The importance of the mass difference in a nuclear reaction is emphasized.
The third section of my course is on kinetic principles in analytical chemistry. I t begins with a discussion of nuclear reactions with the exact decay and activation equations being explained. Since these can be verified in the lab with little difficulty, they are a good start toward the discussion of kinetics. The next portions of the course are devoted to chemical kinetics, always from the viewpoint of what can be done with these phenomena and not what theories can be invented to explain them. Diffusional phenomena are developed, since they will figure prominently in the later treatment of chromatography. Convection, mixing, and sedimentation arc also covered. The treatment of solution reaction kinetics includes a review of organic and redox reactions useful in analysis, followed by a discussion of coordination chain reactions. Here the concepts of a catalyst and an inhibitor can be explained using chemical species with simple structures, which makes it easier for the students to understand enzyme reactions, which come next. At least half an hour, perhaps a whole lecture, should be devoted to exploring the possibilities of enzyme-controlled reactions, especially if no biochemistry course is offered to the students. Of course, examples
46 A · ANALYTICAL CHEMISTRY, VOL. 42, NO. 14, DECEMBER 1970
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of methods are brought in, such as those based on differential reaction rates. Finally, heterogeneous kinetics are treated, with most of the at tention to precipitation and electrode reactions.
The fourth main division of my course is on the principles of ins t rumental techniques and instrumentation. I will say little about this section because I have few innovations to offer. I t should be emphasized t ha t I do not spend time on spectral interpretation— this is covered by the organic chemistry courses—but rather emphasize how the instruments work, sources of error, and so on. The instrumentat ion section will include some basic electronics if the lack of background of the students requires it.
The final section of my course is devoted to separations. Some elementary techniques are covered first, such as extraction, precipitation, and dist i l lat ion/volati l ization, with examples including the Kjeldahl and Pregl methods. Next comes a discussion of chromatography. After a brief introduction to the types of chromatography, the theory is developed. M y t rea t ment is a condensation of the first three chapters of Giddings' book (9) with emphasis on how each aspect of the theory relates to the operating conditions and results in one kind of chromatography or another. The techniques of liquid and gas chromatography are then discussed further as such and finally there is a section on separations based on kinetics, including electrophoresis and dialysis.
The Laboratory
The laboratory in analytical chemistry should not contain repetitious determinations. Each exercise should have the purpose of illustrating a principle, a technique, and, if possible, an application as well, and there should be a minimum of duplication of purposes. I won't t ry to list everything t ha t we do in our lab—or t h a t I would like to see done—but just some of the things I feel are most important . I t hasn ' t proved possible yet to come up with a really ideal group of experiments illustrating all-im-
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portant principles; more development of effective analytical chemistry experiments is necessary, I believe.
We start with a short group of volumetric determinations : a chloride using the Fajan's indicator to check the student's precision, a nonaqueous acid-base titration which ties in with the lecture discussion of this topic, and EDTA titrations of calcium in CaC0 3 unknowns and in dried milk. The procedure in the latter is an old one (10), which, however, is very effective in showing a multistage separation procedure that is clear-cut, quick, and reliable. I just wish I could get some powdered milk unknowns with distinctly different calcium contents.
In the second group of experiments, the students separate and determine a lanthanide-thorium-uranium mixture by anion exchange on a sulfate resin—again something which is being developed in the lecture. Glucose is determined using the enyzme-catalyzed method. The students determine the effect of pH on the polarography of an organic compound and choose the optimum pH for quantitative analysis for the substance (a different one for each student preserves the novelty of what might be repetitious and dull if all were getting the same data on the same compound). A gle column is made and tested. The students have used gc in the organic course, hence this type of experiment in the analytical course. Each group of students uses a different type of stationary phase so that in the end interest is generated in comparing the properties of different columns.
Finally in the first semester we have a group of experiments in which the student is more or less on his own as far as the amount of instructions he is given. One experiment is a straightforward qualitative-quantitative analysis of an organic unknown. The nmr and mass spectra are run for the student, while he or she obtains ir, uv, and gc data himself. The second experiment in this group is an atomic absorption determination of the trace metals in ores and alloys
taken from our stock assembled some 20 years ago and no longer used as unknowns for the major constituents. The students each get six or seven samples of varied composition (iron, zinc, nickel, chromium ores, steel, brass, bronze). They must find a method of dissolving each sample, prepare a set of standards, and determine the six elements on our chromium-to-copper multielement lamp. The final outcome is interesting to analyze, since we give out three or four portions from each sample, and can therefore compare results between students and even for the same student doing duplicates without knowing it.
The final exercise is a miniature research project which requires a minimum of equipment and chemicals. The student is given a mixture of compounds of three metals. The identity of the metals is known to him. He must devise a method for determining the first metal in the presence of the other two by some kind of EDTA-type titration using masking and/or separations. He finds a possible procedure in the literature or perhaps works one out himself from literature data (8). He tests his procedure on a known, revises the procedure if necessary —sometimes discarding it completely and starting out fresh with a new one—and usually makes an attempt at the unknown within the time limit of four 4-hr laboratory sessions. A report is required in journal format, in which the student describes and discusses his work. An important point is that while each student has a different combination of metals, they are all using the same kind of chemistry. This seems to encourage discussion and generates enthusiasm even on the part of the students who had lacked interest otherwise in the laboratory work.
The second semester of the laboratory is devoted primarily to instrumentation. I have not been in charge of this part of the course, and hence my comments on it will be brief. The properties of electronic circuitry, especially operational amplifiers, are investigated. Applications to various techniques
are then brought in as illustrations. An experiment which is instructive and interesting has the students study the effect of changing various parameters (slit width, gain, scan speed) on infrared spectra.
Conclusions I believe that a case can be made
for analytical chemistry as an independent part of the undergraduate chemistry curriculum. To do this, however, the present goals and contents of the basic analytical courses must be changed. A picture of analytical chemistry must be presented to chemistry students which emphasizes our subject's general contributions. The specific details should be saved for students majoring or specializing in analytical chemistry.
I have outlined the analytical principles I feel are most important. Although some of these concepts are relatively sophisticated they can be mastered—even by the1
average student—if presented properly. The student gains an understanding of the phenomena of chemistry which he could not get outside the analytical chemistry course. In short, I believe our students will be clearer thinking chemists and more productive experimental chemists for having had a modern analytical chemistry course.
References
(1) J. R. Piatt, Science 146, 347 (1964). (2) D. J. deSolla Price, quoted in S.
Klaw, "The New Brahmins," Apollo Eds., New York, Ν. Υ., ρ 256, 1969.
(3) W. I. B. Beveridge, "The Art of Scientific Investigation," Modern Library, New York, Ν. Υ., undated.
(4) D. E. Long, Anal. Chim. Acta 46, 193 (1969).
(5) G. W. Ewing, "Analytical Instrumentation—A Laboratory Guide for Chemical Analysis," Plenum Press, New York, Ν. Ϋ., 1966.
(6) T. Coor, J. Chem. Ed. 45, A533, A583 (1968).
(7) H. S. Prank, Science 169, 635 (1970). (8) A. Ringbom, "Complexation in Ana
lytical Chemistry," Interscience-Wiley, New York, N. Y., 1963.
(9) J. C. Giddings, "Dynamics of Chromatography," Part I, Marcel Dekker, Inc., New York, Ν. Υ., 1965.
(10) R. Jenness, ANAL. CHEM. 25, 966 (1953).
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