a place for cherni~t~
edited by: FRANKS. QUIRING Clayton High School Clayton, Missouri 63105
Analytical Chemistry Michael D. Seymour Hope College, Holland, MI 49423 I t is important to realize that in the practice of his or her profession the analytical chemist uses a wide variety of experimental procedures. The field of chemistry has traditionally been divided into the major disciplines of analytical, inorganic, organic, physical, and biochemistry. Today, however, there is a large amount of overlap among the various disciolines as seen bv" ioh descrintions for chemists in areas such as physical-organic, environmental, analytical, hio-inorganic, oreanometallic. as well as medicinal. clinical. and ~. o l.v m e r ch'emistry. In v'iew of such a multidis~iplinar;marketplace. it should be understood that an effort todrscril~etheactivities of the analytical chemist is meant only to he suggestive and by no means limiting. What is Analytical Chemistry? Analytical chemistry basically deals with the qualitative and quantitative identification, characterization, and measurement of the chemical species present in a sample. The measurement process can range from standard techniques for routine quality control to state-of-the-art techniques used for fundamental studies. However, regardless of the measurements made, the actual experimental determination of a given chemical species is only one aspect of a much more comprehensive analytical procedure which takes into account: 1) definition of the problem and the manner in which chemical analysis will be relevant to its solution, 2) identification of the amropriate chemical species to be mea.. .
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3) collection and nreliminarv treatment of the samole. 41 selection ofa suitahle measurement technique a i t h respect to i p n w s voncentrstim,accuracy, precision, cwt and time, 5) separation of the desired species if interfering components are
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6) measurement of the concentration of the species 7) evaluation of the data, and 8) communication of the results.
A closer look a t each of these individual operations will provide an idea of the diversity and challenges involved with the problem-solving aspect ofanalytical chemistry. The first three of the above operations will often not he under direct control of the analvtical chemist. but will be the responsibility of the person, or Aient, requesting the chemical analysis. This, however, does not mean that these operations can he neglected. The analytical chemist should obtain as much information as possible about the client's problem, the way in which the chemical data are to he used and interpreted, the general composition of the sample, and the manner in
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This feature surveys the diversified careers which are available to chemists or which require some chemical baining. We are all career consultantsto some degree. This feature may supply some new insights as to what is available.
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Journal of Chemical Education
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which the sample was collected, stored, and treated. This overall understanding of the problem and the sample is a necessary prerequisite for choosing a measurement process which will provide both the desired information and therequired level of reliability in terms of accuracy and precision. Choice of the optimum experimental p r d u r e is a decision for which the analytical chemist is uniquely qualified. The wide variety of problems encountered by the analytical chemist requires the use of methods which range from traditional wet chemistrv to modern instrumentation. Com~endia ot analytical methods provide ideas as to what techniquks may be most applicable, but it is up to the analytical chemist to organize creatively the appropriate methods into a procedure which works well for thesamolesat hand. The method ielertion and experimental design must be based on previous experience, general knowledge of the chemical reactions involved, the desired accuracy and precision of the data, and the suitability of various instrumental and wet chemistry procedures. In situations where more than one type of procedure is capahle of providing the requisite precision and accuracy, the anslytical chemisi must use costlbenefit considerations in choosing the least expensive way of obtaining the desired information. For example, the benefit associated with anexpensive, highly accurate, and very precise quantitative analysis of drinking water for a component which may affect human health is worth the cost, but the benefit of an equally expensive, accurate, and precise analysis for a component which only imparts a slight odor to the water may not justify the cost when a less expensive, less accurate method can provide the required information. Analyses which are more accurate than the situation warrants can be costly and wasteful in both time and resources; while, on the other hand, analyses that lack the necessary accuracy are of little use. Other factors which enter into the costlbenefit consideration are the time required for a sinale determination and the total nttmher of dete;minations LO be performed. The overall impact of these two factors is often reflected in the choice between wet chemistry and instrumental procedures. While wet chemistry procedures such as titrations and nravimetric methods offer low cost with good accuracy and precision for high concentrations of selected components, they may be lengthy if many samples are analyzed. instrumental procedures, on the other hand, are generally more expensive in terms of initial cost, offer lower detection limits with some loss in precision, and require less analysis time per sample, which can make them cost effective for laree numhers of samnles. ~ ~ ~ - - The experienced analytical chemist wiylrekize that the proper use of both instrumental and wet chemistrv methods complement each other and will make extensivkuse of both. Since most s a m ~ l eare s reallv com~lexmixtures thev often require some type of clean-upprocedure in order toisolate effectively the component of interest, or analyte, from other ~
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components which may interfere in the analysis. In order to avoid time, expense, and possible loss of any analyte due to lengthy isolation procedures the analytical chemist should develop efficient separation schemes. The separation may reouire the comhination of several standard methods into a - ~ unique procedure for the matrix of interest. For example, the vanadium content in a new d o v mav be critical to its p h ~ s i d ~-~ properties. While methods fo;det&mining vanadium exist, none of them may be suitable for the new alloy. Thus, the analytical chemist would need to develop a procedure which would be suitable for this new matrix. After the appropriate collection and separation steps have been taken, it is the measurement process used in the laboratory which finally provides data on the analyte concentration. The quality of the experimental data will ultimately depend on the ability of the person performing the measurements. In many cases the data will not be obtained by the analytical chemist, but rather by personnel trained specifically for that purpose. These technical personnel, or analysts, need not be c6nc;rned about the overall scopeof the prohlem, but should focu on the quality of data, ensuring that it is acquired with the best possibie accuracy and precision inherent to the method. The position of analyst is one frequently filled by bachelor degree chemists, since a general background in chemistry is needed to learn effectively and understand the snecific ex~erimental~rocedwesused in anv ~ v e laboratow. n xlthoughihe job of analyst is not as invofvid as that of the analvtical chemist. it is verv demanding- and reauires a high degree of pr~ficie&~. After the data have been acauired they must he converted to a form which is relevant to the problem, such as absorbance readinas being converted to the weight of analyte - percent present in the original material. For many routine experiments acauisition of the raw data and conversion to meaningful reSUI;S is automaticd1y cinrried out by computers, but the fact that a result iscalculated to 12diaitsdoesnot mean that it is correct. The analytical chemist should have some intuitive, common sense feeling for the quality of the data based on past experiences. Thus, he or she should be able to identify those results which may indicate erroneous procedures. In addition to calculating the final result, it is essential that the analytical chemist calculate the reliability of the result in terms of precision and accuracy. The random errors associated with precision will tend to cancel one another when a large number of measurements are made. but determinate errors such as ODerator, instrumental, or &ocedural bias which affect accuracy do not cancel and will offset the exnerimental results from the K e results. By proper use of sta&tical procedures the analvtical chemist can determine the extent of random and determinate errors and consequently design or re-design experimental procedures which maintain the required accuracy and precision. The degree of uncertainty indicated by the accuracy and precision must also be communicated to the client. This allows the client to arrive a t an interpretation of the data which is consistent with the experimental procedures and which also takes into account any limitations associated with the data. The analytical chemist must oversee a large number of operations in the process of performing a chemical analysis. The task of selectine the hest orocedure for a riven andysis &&be compared toselecting h e best path through a maze. In selectine a oath through a maze. there are manv directions in which to proceed and one may encounter many k o n g turns and dead ends. The task however becomes much easier if one has an overview of the entire maze and clearly knows in which direction to proceed to find the end. Similarly, for a chemical analysis, there are many procedures whichmay be used t o obtain the desired information, but selection of the best procedure becomes easier when the problem is clearly defined and the requirements for the data well established.
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Career PlannlnaStudents interested in analytical chemistry should realize that the discioline is hoth applied and fundamental in nature. The applied concept uses kstablished procedures t o obtain information about a soecific problem. while the fundamental concept is concerned with overcoming problems associated with thedevelooment of new toolsand techniques with which to better investigate the physical and chemical properties of materials. The new knowledge which is obtained as a result of fundamental studies has the potential to improve the applied aspects of the discipline. While the applied studies are eenerallv" found in industrial settines "~and the fundamental studies in academic settings, there are no fixed dividing lines and both a ~ ~ l i and e d fundamental studies are carried out in both settings. Regardless of the setting or the type of work,, the analvtical chemist will be Dresented with challenainz opportunities to investigate new and interesting areas, to overcome unforeseen technical and chemical difficulties, and to gather original information in response to unique questions. With the rapid development of computer technology, opportunities for analytical chemists promise t o be even more excitina and demanding, In a special report on the future of analytGal chemistry', ;rhomas lsenhour comments on the future of computers in analytical chemistry, "It looks great. The table has been set for a feast of new analytical chemistry." To prepare for a career as an analytical chemist or an analyst, students should take as much math, chemistry, and physics as possihle in high school. At the college level the student should take courses required for a chemistry major, as well as courses in statistics, electronics, and computer science. Courses which deal specifically with analytical chemistrv. instrumentation. or seoarations should be taken if they arLnot included in the chemistry major requirement. Independent research should be part of the student's program if it is at all possible, because it is through this type of activity that the student learns how to define a problem and to develop a systematic approach for obtaining the data needed to address the oroblem. While the formal training offered a t the undergraduate level cannot turn out students-ready to attack every type of problem (and is not intended to), it can provide students with both a sound background of fundamentals on which to base decisions and a confidence in one's ability to gather accurate, reproducible data. Education a t the undergraduate level will, in most cases, be appropriate for a student to seek employment as a technician. h r students who wish w seek wsitions with a broader range of reponsibilities and to develop self-directed research programs it will be necessary to obtain a master's or, preferably, a doctoral degree. Many graduate programs are structured such that the student can proceed directly from the bachelor's degree to the PhD without earning a separate master's degree. In graduate school, the student will generally take courses which have a strong emphasis on analytical methods, such as sepruations, spectroscopy, electrochemistry, electronics, or solution equilibria, although many other specialized courses are offered. The PhD is a research degree, so that a maior portion of the student's activitv will be involved with a un:qu> research project under the direction of a professor who serves as the student's mentor during the course of the studies. Students who are thinking about attending graduate school should also be aware that there are a reasonable number of graduate teaching assistantships available which pay stipends. Upon completion of the PhD the analytical chemist may ~roceedinto a variety. of governmental, industrial, or academic positions. An extensive survey of salaries for chemists is given in the July 11,1983 issue of Chemical and Engineering A'eu. ~
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' Isenhour, Thomas, Anal. Chem., 55,824 (1983).
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Number 3 March 1984
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While the ioh descriotions will varv.ereatlv. - . the activities of the analyiical chem'ist most often will involve answering auestions which deal with various a s ~ e c t of s the overall ana&tical procedure outlined a t the he&nning of the article. T o
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Journal of Chemical Education
orovide the best answer to these auestions. the analvtical chemist must have a critical attitude toward'the techniques and ~rocedureswhich are used and the results which are obtained.
