and REVOLUTION
A
nalytical chemistry is an ancient science (14).For more than a hundred years, it has played an important role in chemical education. The curriculum used to teach analytical chemistry has, of course, changed dramatically over time, from the use of books that described the use of gravimetry, flame tests, and bead tests to computer simulation of actual analytical instruments and experiments. Understanding the origins of the analytical cumculum is essential as educators debate how it should change to meet the needs of today’s students. In this Report, the evolution of analytical chemis try into the 20th century is briefly traced to lay the foundation for discussing the evolution of the modem cumculum and where it might be headed.
To determine in what direction the analytical chemistry curriculum shouldgo, it’s important to look back at its origins
In the beginning The tools and basic chemical measurements of analytical chemistry date back to early recorded history. The chemical balance is of such early origin that it was ascribed to the gods in the earliest documents found. The use of standard weights is traced to the Babylonians in 2600 BC, who considered them so important that u 4 ers were supervised by their priests. Metals and allays were also used in ancient times, and the perceived value of gold and silver was probably a major incentive for acquiring analytical knowledge. In the fourth century BC, the purity of gold was determined from the extent of the yellow marks it made on a touchstone.
Gary D. Christian University of Washington 532 A AnalyticalChemisfry, September 1, 1995
0003-2700/95/0367-532&$09.00/0 0 1995 American Chemical Society
IN Q U m A m ANALYSIS The first wet test appears to have been described by Pliny the Elder (AD 23-79), who noted that if copper sulfate was adulterated with iron sulfate,the extract of gallnuts turned black. During the Middle Ages (ca. 470-1470), alchemists began to assemble the body of knowledge that became analytical chemistry, and growth continued during the phlogiston era (to ca. 1700) as quantitative chemical relationships were sought. Robert Boyle coined the term “analyst” in his 1661book The Scegtical Chymrist,so he could be considered the creator of this branch of chemistry as well as the founder of chemistry as an independent science. Gravimetric analysis was probably invented by the German physicianchemist Friedrich Hoffmann in the 17th century when he precipitated chlorides with silver nitrate and sulfates with lime. In the 18th century, Jons Jakob Berzelius inboduced stoichiometricconcepts, and Antoine h o i s i e r used the balance to disprove the phlogiston theory by performing quantitative experiments to demonstrate the law of conservation of mass, which earned him the title “father of quantitative analysis.”The 18th century also saw development of chemical microscopy, flame tests, the blowpipe, bead tests, and tihimetry. Joseph Gay-Lussac, Robert Bunsen, and Karl Friedrich Mohr developed titrimetric analysis in the 19th century. In fact, Gay-Lussac developed a titrimetric method for silver that was accurate to better than 0.05%and has not been improved upon since (5).The only major advance in titrimetry in the 20th century was the infroduction of complexometric techniques.
In the h t 40 years of the 20th century, the emphasis on a scientific, rather than an empirical, approach increased, as did the emphasis on instrumentalmeasurements to sumdement traditional wet chemism mea .. surements (2).During this period, several academic centers of analytical chemistry emerged, and such notable academicanalytical chemists as C. P. Baxter (Harvard), E. M. Chamot (Comell),C. W. Faulk (Ohio State), N. H. Furman (Princeton),V. W. Meloche Wisconsin). M. G. Melon (Purdue), E. H. Swift (Caitech),G. F. Smk i mli nois), H. H. Willard (Michigan), J. H. Yoe Virginia), and I. M. Kolthoff (Minnesota) began to develop analytical chemistry as we know it today.
”lV
m m i m i a i m CKUNWU;M m
‘““,YTISCHEN CHEMI 11*>TmlT
W. O S T W A L D .
The early textbooks
Textbooks on analytical chemistry began appearing in the 19th century. Karl Frese nius published a book on qualitativeanalysis (Anletung zur qualitntiwen chemischen Analyse) in 1841, followed by a volume on quantitative analysis (Anletung zur quantitatiwen chemischen Analyse) a few years later. In 1894, Wilhelm Ostwald published an influentialtext on the scientific fundamentals of analytical chemistry entitled Die wissenschajichen Grundagen der analyiischen Chemie. He was the h t to recognize the role of analytical chemistry in the development of chemistry as a science, and he put forth theoretical explanations of analytical phenomena, including equilibrium constants. He stated that “Analvtical chemishv is doomed to continue occupying a position subordinate to other branches if analytical chemists do not stop teaching and practicing analysis solely as an empirical technique and art.”
Title page lrom Die wissenschaflichen Grundagen der analytischen Chemie.
Frances Sutton wrote A Systematic Handbook of VolumetricAnalysis (or The Quantitative Determination of Chemical Substances by Measure, Applied to Liquids, Solids, and Gases) in 1863. By 1911, the book had gone through 10 editions (7). which indicates the rapid changes in volumetric techniques during that time. (Re member, this was in the days before books were revised frequently.) The 621-page 10th edition is filled with details on volumetric apparatus, specifictechniques for given substances, and titrimetric methods such as alkalimetrv and acidmetrv. ,. oxi. dation and reduction, and precipitation. The 6rst edition of Stephen Popofps Quantitative Analysis lists three reasons for its publication: “First, to incorporate in
Analytical Chemistry, September 1, 1995 533 A
a single book the theory, laboratory instructions, problems, and explanations for the calculationsof these problems: second, to emphasize the law of mass action and the theory of equilibrium to quantitative reactions; third, to incorporate some of the more recent advances in analytical chemistry.”The second edition, published in 1927 (8).includes chapters on errors and compilation rules, electroanalysis, conductomeric titrations, and colorimetric methods. Recognizing the importance of acquiring an understanding of the basis of a measurement, Popoff states, ‘“The ob ject of teaching chemistry in a college or university is not to turn out mere routine analytical chemists.” In their classic 1929 book Applied InorgunicAnalysis, W. F. Hillebrand and G. E. F. Lundell of the National Bureau of Standards (now the National Institute of Standards and Technology), stated that . . there is a great need for the develop ment of quantitative procedures that can he applied to the separation or determination of substances in complex mixtures.. . .”They were refemng, however, primarily to precipitation procedures. Colorimetric methods for inorganic analysis were sufficiently mature by 1921 that F. D. Snell devoted a book to that sub ject. The second edition, published in 1936with C. T. Snell,was expanded to two volumes and also included organic and biological methods (9). It contained numerous designs of Duboscq and similar
colorimeters,including a “universalcole rimeter” for nephelometric as well as cole rimetric measurements, and a Yoe design for a photoelectric colorimeter. A classic The person who unknowingly laid the foundation for much of the renaissance of analytical chemistry in the United States was Nicholaas Schoorl. a professor in the School of Pharmacy at the University of Utrecht (The Netherlands), who taught analytical chemistry and studied the characteristics of acid-base indicators and derivativesof dilute acids and bases. One of Schoorl’s students was Izaac Maurits Kolthoff,who majored in pharmacy rather than chemistry to avoid the Latin and Greek requirements of the chemistry department.
“The main emphasis should be on the hndamentak chemical aspect.”
‘I.
I
Piate of pholoelectric colorimeter Colorimetric Methods of Analysis.
Kolthoff became interested in the t h e ory of acid-base indicators (4) and was greatly influenced by a 1909 paper by S.P.L. Sorenson on the colorimetric and potentiometric determination of pH. Schoorl, a modest man, insisted that Kolthoff publish his early papers under his own name, and Kolthoff published his first paper, entitled “Phosphoric acid as mone and dibasic acid,” in 1915 (IO).He presented his thesis in 1918 on “Fundamentals of Iodimetry,” a subject he would return to often. He spent 10 years on the faculty in the Pharmaceutical Institute at the University of Utrecht. publishing 270 papers and 3 books before joining the faculty of the University of Minnesota in 1927. Although Kolthoff officially retired in 1962, he remained active in analytical chemistry for another 30 years. Kolthoff himself felt that the transformation of analytical chemistry into a scientific discipline came about because of physical and b i e physical chemistry (4)
534 A Analytical Chemistry, September 1, 1995
The teaching of analytical cnemistry in the United States was markedly influenced by the publication of Kolthoff and Sandell’s Tat6ook of Quantitative InorgunicAnalysis in 1936, which did much to estahlish analytical chemistry as a separate discipline. In the preface, Kolthoff and Sandell note that “It does not seem to be generally realized that analytical chemistry is one of the fundamental branches of science.”Their goal was to offer a halanced outline of the theoretical aspects of inorganic quantitative analysis, noting that ‘There appears to be a tendency to exag gerate the significance of ‘theory’ at the expense of practical work in chemical analysis.” (Kolthoff, of course, is known for his maxim that “theory guides, experiment decides.” One wonders if he might have borrowed this from Robert Boyle, who stated in The Sceptical Chymist that ‘“Theories must be supported by experiments.’? In their first edition, Kolthoff and Sandell emphasized classical procedures, but “highly specialized” methods (conductometric and potentiometric titrations, gas analysis, nephelometry, spectrography, etc.) based on physicochemicalproperties were detailed enough to enable the student to “appreciatethe advantages of such methods.”The third edition in 1952 still emphasized the classical techniques (11). The authors note that “It might seem that because of the development of selfregistering instruments and automatic apparatus, classical analytical chemistry is becoming outdated. If this idea were correct, the subject matter of our courses in quantitative analysis would require drastic revision. In our opinion such a change is neither necessary nor desirable. . ..The main emphasis in beginning courses in quantitative analysis should be on the fundamental chemical aspect.” Moving into the modern era There have been several surveys in the past decade that have summarized the re cent evolution of analytical chemistry and what is covered in modem analytical chemistry texts (12,13).In preparation for a symposium on teaching analyticalchemistry organized by Royce Murray in 1980, I surveyed 25 major institutions to determine what was being taught at the undergraduate level and when.
In my survey, about 40% of the schools taught analytical chemistry in the freshman year. The quality ranged from desirable. in which analytical faculty taught a lectureflab course using a quantitative analysis test, to undesirable, in which nonanalytical faculty taught a lab only, with no connection to the freshman lecture course. Typical freshman or sophomore analytical courses used texts that covered gravimetric and volumetric method acid-base equilibria, spectrophotometry (W-vis, atomic, In), potentiomehy, and separations (solvent extraction,basic chi matography). Lectures typically covered these topics, and occasionally ion exchange, GC, ion-selective electrodes, nonaqueous acid-base chemistry. electro gravimetry, and fluorescence were discussed as well. At the symposium, Murray summarized five major factors that had affected the teaching of analytical chemistry over the past decade: employment opportunities, because the number and complexity of analyses had grown as a result of increased government regulation: increased student interest; increased faculty appointments; continued grant support for fundamental research in analytical chemistry. even though the pressure to fund applied science had increased; and the knowledge explosion in fields such as chromatographyand data handling. The knowledge explosion is the bipgest problem with which analytical chemistry educators must contend, with too little lecture and laboratory time available to teach properly. Murray noted that textbooks have grown more in size and number of chapters than they have in terms of conveying knowledge. He pro posed that we move a greater portion of what we customarily call "instrumental methods" to the sophomore year and r e move material on the less-relevant titrimetric and gravimetric methods. There are those who argue, however, that we must be careful not to displace a thorough coverage of conventional equilibriumand related topics, and that the increased interest in biological and pharmaceutical sciences and the importance of being able to apply equilibrium methodologies to experiments in these areas underlines the need for students to receive a firm grasp of these methodologies.
Table 1. Subjects taught in quantitative analysis lecture 2 90%
3%
#"-,3% 6049% 50-59% 40-49% 30-39% e 30%
Signhcant 1,gdres.conhdence ,m"0-test,concentration unlts, neutral zatton titratmons, bulfers. polyprotc ac ds, pr,mary standards comolexomemc iitratmw .K redox t~lranonsNernst eodat~oncei I-Test,>onicstrengtn. actwty coetlaent. gravmetry, Dack titrai ons. acid-base theory salt hydmlyss a-values, siandaro solutions K,. soILbditY. charae balance redox eauahons. relerenca ana other electrodes, spihrometry Error propagation, Debye-Hiickel, diverse ion effect, normality, precipitation titrations, mass balance, formal potential. ion-selective electrodes, standard buffers. mixture calculations In spectrophotom, Sampling, sample preparation, least squires, permanganate and dichromate titrations, junction potentials, standard addition, atomic spectrometry,chromatography, ion exchange, GC Glassware calibration, iodimetry. derivative tiirations, elmr ravimeti coulometry, soivenl extraction, LC, theoretical plates, res2ution f-Test, Kjeldahi, cerate titrations. polarography and voltammetry, van Deempter equations Correlation coefficients, amperometry, IR, fluorescence. chelate extractions,capacity factor, TLC, planar chromatography Control charts, Gan's plots, anodic stripping voltammetry, spectral iqterpretation, JCDcnartmernnw k n rhmms+nnrsnh\r rnmni >tar rogramming
In 1984, I conducted a survey (sent to 175 schools, 95 responses received) to help in revising an ACS exam in analytical chemistry. Respondents were asked to check which of a list of 100 topics they taught in their quantitative analysis course. Apartial summary of the results is given in Table 1. Interestingly. not a single topic was checked 1Wof the b e . m e top 30% of topics were generally classical methods, statistics, potentiometty, and spectropho tometry. Atomic spectrometry and chro matography were in the next IO%,and more specialized electrochemistryand chroma. tography in the following 10%.The lower 50% included some higher level instrumental methods such as voltammeby and In S ~ ~ ~ ~ ~ O S C O P Y . h c k e and Grossman conducted a survey of the cuniculum in quantitative analy sis in 1987 and compared their results with the 1982 ACS exam in analytical chemistry (14)).They noted that all the popular texts included virtually the same topics and that all the schools offered either a one-semester or a one-quarter quantitative course. They concluded that, although lecturers do not feel constrained to slavishly follow the emphasis in their assigned texts, the range of topics clearly does follow the texts. They compared some earlier texts with modem ones and found that, although there was far greatei emphasis on gravimetric analysis and a p plications of redox titrations in older text-
books, the distribution of pages among other topics generally was not too different from that in contemporary texts. However, although the earlier texts reflected what analytical chemists did, culrent texts do less so and seem to have evolved directly from their predecessors with expanded coverage of statistical methods and addition of some instrumental techniques. Traditional determinations continue to be the mainstays of the laboratory part of the course. Murray has also documented the content of undergraduate analytical chemistry courses from the 1950s. when rapid changes began as a result of what he calls "chemical transducers," devices and means to convert chemical structure and composition information into electrical and optical phenomena such as spectra, voltammograms, and chromatograms (15).He asserts that an appreciation of chemical transducers is perhaps the most lasting contribution that analytical chem. istry plays in undergraduate education. During the period 1930-50. texts covered basic chemical reactivity and physical aspects of titrimetry and gravimetry. In the 196Os, spectrophotometry, separations, and electrochemistry were added, and coverage of gravimetq decreased. Although the emphasis on titrimetry has remained constant over 40 years, coverage now includes more quantitative treatment of chemical equilibria, reactiv-
Analytical Chemistry, September 1, 1995 535 A
ity, and use of electrodes as transducers for detecting end points. It is clearly pedagogically correct to further enhance the emphasis on instrumental analysis in the introductory-level analytical course. However, there are roadblocks to introducing more chemical transducer materials to the sophomore level introductory course: obtaining the necessary lab equipment, changing the content of the preceding general chemistry course, and deciding what to remove from the analytical course to make room for the new material. Therefore, evolution of the course may rest as much on the school’s (or faculty’s)priorities in expenditures as it does on intellectual progress in the field or the contents of textbooks. In addition, the content of the general chemistry course must be enhanced to provide the proper background for introducing chemical transducer material in the analytical course. To lead or to follow?
The ACS analytical exam more or less represents what is taught in quantitative courses (the topics covered on the 1988 ACS exam reflect the results of my survey). However, there are those who argue that the ACS exam should concentrate more on instrumentation to encourage instructors and authors to change their ways. How should analytical chemistry be taught? The question of how to teach analytical
chemistry is a somewhat different one from what should be included in textbooks or in the curriculum. John Wright at the University of Wisconsin notes that the elementary analytical course is probably pretty good at what it does but is somewhat outdated. In contrast, the instru-
It is pedagogically correct to enhance the emphasis on instrumental analysis in the introductory-level analytical course.
Should standardized exams reflect what is taught in our curriculum or should they take the lead in shaping the curriculum? The Graduate Record Exam (GRE) must necessarily reflect, to the extent possible, what is taught, because it is used to test students’ competence for advanced study based on their knowledge of their undergraduate curriculum. For several years, I was a member of the GRE Committee of Examiners for the Chemistry Test and, mental course has quite a ways to go. until just recently, there was only one r e p What we need to do is to teach students to resentative for analytical chemistry and be better problem solvers. Although the two representatives each for organic, inbest students can readily handle the tradi. organic, and physical chemistry (there are tional approach of assimilating lecture now two analytical representatives). The notes, doing practice problems, and studyareas emphasized in the exam approxi- ing the text, others need to be taught the mately reflected the population of the skills of thinking scientifically. The probcommittee: 15%analytical chemistry, 25% lem is that innovative approaches to deinorganic chemistry, and 30%each or- velop “mind penetration strategies” reganic and physical chemistry. The analytquire an increased commitment from both ical portion of the exam included the clas- faculty and students and are inherently sical quantitative areas of titrimetry, sepatime inefficient. rations (gravimetry and theory and A successful method developed by applications of chromatography), data John Walters at the University of Wisconhandling, statistical tests (1, F, Q, chisin (now at Saint Olaf College) uses a square), and standards and standardizagroup or team approach in the laboratoly. tion techniques. Instrumentally oriented At Wisconsin, students form teams of topics included basic electronics, electro four and work on specific problems that chemical methods, spectroscopic meth- might be encountered in developing an ods (electromagnetic, mass, NMR), and experiment. For example, If,, might be radioactivity. used to calculate solubility losses in a 536 A
Analytical Chemistry, September 1, 1995
gravimehic determination. Although students may have encountered these calculations in the lecture portion of the class, the change in context makes a big difference in how they approach the problem. The group approach creates discussion, participation, and responsibility to the team, and role playing allows the students to experience different sets of responsibilities (16). Walters has been an innovator in the way analytical chemistry is taught. By us ing role playing in the laboratory. he creates an atmosphere that encourages a sense of “ownership” of the experiment. Other educators relate the excitement of recent discoveries, by their own research group or others, to the students. Discussions of this sort do more to instill in students the character of chemistry than does learning new factual material. F I A Mini analytical chemistry?
There are sound pedagogical reasons for keeping much of OUT time-honored curriculum the way it is. However, I would like to propose (and I admit my bias up front) introducing a semiautomated, miniaturized, and highly efficient technique into the quantitative analysis laboratory: flow injection analysis (FIA). Conceived in the mid-l970s, FIA has proved to be a versatile tool for performing wet chemical analyses on a microscale level and in a short
Figure 1. Single-line FIA manifold.
Analog output is in the form of a peak that starts recording at the time of injection 6.Tis the residence time corresponding to the peak height measurement and t, is the peak width at the baseline.
time frame (17).Although there are more than 6000 publications on the topic, an indication of its popularity in the research community, FIA is not widely used in the teaching laboratory. Ruzicka and Hansen began to incorporate FIA into the teaching laboratory shortly after its development as an analytical technique (18).Since then, equipment has been improved and made less expensive,and modem computer technology has made it easy to automate. Several suitable laboratory exercises have been published (19-20. The potential of FIA in chemical education has been espoused by several educators (28,ZS), and the University of Kansas has received funding to introduce FIA into its laboratory courses and those of surrounding colleges. The basic components of an FIA system are a pump, an injector, a reaction coil, and a detector (Figure 1).A peristaltic pump is generally suitable. Tube diameters are typically O.H.8 mm, flow rates are 1ml/min, and injected sample volume is -25100 pL. The carrier stream into which the sample is injected is unsegmented and may contain a reagent that reacts with the analyte. As the sample is propelled by the carrier stream, it undergoes controlled dispersion and mixing with the carrier, depending on the manifold design, resulting in a concentration gradient of the sample. The products of the reaction are monitored by a detector with an appropriate flow cell, and a transient peak is recorded in 30 s. Typically, the height of the peak is measured and related to the analyte concentration, although area or width may be used instead. The FIA manifold can be config ured in a variety of ways, from a single channel to multiple channels. so multiple reagents can be used. For those who wish to introduce FIA into the laboratory. a fairly simple manual system can be assembled, and inexpensive manual and computercontrolled systems are commercially available. The manual FIA system shown in Figure 2 contains avariable-speed peristaltic pump, an injection valve, a Tsonnector for a twe line system, and a reaction coil, and can be connected to an appropriateflow cell or detector to perform a variety of experiments. Such a manualiy operated system
-
-
Figure 2. Manually operated FIA Instrument.
is preferred for student experiments because students can get hands-on experience in its operation. What can be done with FIA in the quantitative analysis labomtow? Spectrophotometric measurements can be performed in a fraction of the time required for conventional spectrophotometry. In fact, a comparison of the two can be revealing to students. In conventionalspectrophotometry, each sample must be measured and added to the reagent($, diluted to volume, and allowed to react. An aliquot is retrieved for the manual spectrophotometric measurement, is disposed of, and the cuvette rinsed. In addition, large quantities of reagents are consumed and must be disposed of properly. In the FIA experiment, a stock solution of one or more re agents is prepared and pumped in the flow system. The sample is loaded into an injection valve (not requiring careful measurement by the student) and injected into the flowing carrier stream. The measure mentis completed in < 1 min. Multiple in jections can be readily performed to o b tain precision measurements. Beer’s law still applies in FIA and can be tested. Although the sample is dispersed. the extent of the dispersion can be determined by obtaining a steadystate signal with a large volume of sample or dye that does not become diluted and so absorptivity values can be determined.
Many reactions measured by spectrp photometry, such as those in the molybde num blue method for phosphate determination (30),require a significantamount of time to occur. Because the measurement conditions of FIA are very reproducible, the reaction need not be completed, and the measurements can be precisely performed with the few seconds of reaction that occurs as the sample is being transported to the detector. We have actually performed measurement of an organic condensation reaction in a nonaqueous solvent in 40 s that normally requires up to 3 h using conventionalspectrophotumetry (31).For kinetically slow reactions, stopped-flowmeasurements with computercontrolled timing devices for the pump can be used to measure the rate of product formation, usually in c 1 min. Solvent extraction can also be performed by FIA (32)by injecting the sample into an aqueous carrier that merges with the extracting solvent. These segments are carried to a phase separator as extraction into the organic solvent occurs. After phase separation,the extracted analyte is carried to the detector. This proce dure greatly reduces the volume of organic solvent that must be disposed of, and the extraction and measurement are performed very quickly. In addition, because a closed system is used, students’ exposure to the solvent is minimal.
Analytical Chemistry, September 1, 1995 537 A
FIA “titrations” can also he performed (32).In this method, the carrier is the titrant and contains an indicator. When the sample is injected, equivalency occurs on the rising and falling portions of the recorded signal when passed through a mixing chamber: the width of the signal is proportional to the logarithm of the analyte concentration. Although this procedure has poorer precision than does volumetric titrations, a wide range of concentrations can he measured. FIA can also be combined with classical coulometric generation of titrant (33). For the more adventuresome, the new versatile technique of sequential injection analysis (34, 35) can be introduced to students. This technique replaces the injection valve with a multiport selection valve. Solutions are sequentially aspirated, under computer control. into the r e action coil and then propelled to the d e tector. This advanced experiment would be suitable for the instrumental analysis laboratory.
Words of wisdom
The quantitative analysis course will continue to he important in chemical education. As Lord Kelvin said, “Unless our knowledge can h e measured and expressed in numbers, it does not amount to much.” R. S. Mulliken, 1966 Nobel laure ate, said, “1 think it was in a course in quantitative analysis that an appreciation of the scientific method and its rigors began really to take hold of me. . .There were no shortcuts to beat clear thinking, careful technique, and endless patience. Finally, Popoff obsenred, ‘ m e value of quantitative analysis to a student. . . comes in the acquirement of oatience, neatness, and accuracy” (8) References (1) A History ofAnalytica1 Chemist- Laitinen, H. A,; Ewing. G. W., Eds.; American Chemical Society, Division ofhlytical Chemisby:Maple Press: York, PA, 1977. (2) laitinen, H. A. Talanta 1989,36,1. (3) Kolthoff, I. M. I. Electrochem. SOC.1971, 11X.SC. ~
~
(4) Kolthoff, I. M. Am. Lob., May 1979, p. 42.
.
Order vow NEW Pesticide/ Metabolite Catalog NOW!
.
Produced biennially, the Chem Service Pesticide/ Metabolite Catalog contains the world’s largest selection of pesticide standards. Included in the new expanded listing are the first A2LA Certified pesticide reference materials available anywhere. All Chem Service pesticidehnetabolita standards are purity certified and expiration dated. Each chemical is cross referenced by generic, trade and chemical name, with metabolites listed under their base compound. For a free copy, contact us at 800-452-9994.
ChemService PO Box 3108 * 660 Tower Lane West Chester * PA 19381 CIRCLE 1 ON READER SERVICE CAR0
538 A Aflaiytica, Chemistry, September 1, 1995
(5) Beck, C. M., 11. Anal. Chem. 1991, 63, 933 A. (6) Burns. D. T. FreseniusJ. Anal. Chem. 1993,347.14. (7) Sutton, F. A SysfematicHandbook of Volumefric Analysis. 10th ed. (revised by W. L.
Sutton and A. E. Johnson); P. Blakiston’s Son: Philadelphia,1911. (8) S. Popoff, Quantitative Analysis. 2nd 4.; P. Blakiston’s Son: Philadelphia,1927. (9) Snell, F. D.; Snell,C. T. ColorimefricMethods ofAnalysis, 2nd ed.; Van Nostrand New York, 1936; Vols. I and 11. (10) Kolthoff,I. M. Chem. Weekblad 1915,12, 644. (11) Kolthoff, I. M.; Sandell,E. B. Textbook of QuantitafiveInorganic Analysis. 3rd ed.; Macmillan: New York, 1952. (12) Braun, T.; Bujdos6, E. CRC Crit. Rev. Anal. Chem. 1982,113,223. (13) Braun,T.FreseniusZ. Anal. Chem. 1986. 323,105. (14) Locke, D. C.; Grossman, W.E.L. Anal. Chem. 1987,59.829 A (15) Murray, R W. Talanta 1989.36,ll. (16) Walters, J. P. Anal. Chem. 1991, 63, 9774,10774,1179~. (17) Ruzicka,1.; Hansen, E. H. Anal. Chim. Acta 1975, 78, 145. (18) Hansen, E. H.; Ruzicka,J. I. Chem. Educ. 1979,56,677. (19) Meyerhoff, M.; Kovach, P. M. I. Chem. Educ. 1983,60,766. (20) McClintock,S. A,; Weber, J. R.; Purdy. W. C. 1. Chem. Educ. 1985.62.65 (21) Rim. 6; Luque de Castro, M. D:; Valcarcel. M. J, Chem. Educ. 1986,63,552. (22) Keller, I.W.; Gould. T. F.; Aubert, K T. I. Chem. Educ. 1986,63,709. (23) Stults, C.L.M.; Wade.A P.; Crouch, S. R I. Chem. Educ. 1988,65,645. (24) Stults, C.L.M..etal. I. Chem. Educ. 1989. 66,1060. (25) Kneller. P. E.; Anderson,R M.:Tvson. I. F. Anal. Roc. 19f49.26.48 .~ (26) Nobrega, I. A.; Mozeto, A A.; Alberici, R M. 1. Chem. Educ. 1991,68.966. (27) Tyson, 1.F. A4icmchm.J. 1992,46143. (28) Kowalski, B. R.; Ruzicka, J.; Christian, G. D. TrendsAnal. Chem. 1990,9,8. (29) Ruzidta. I.;Christian,G.D.Analyst 1990, 115.475. (30) Christian, G. D.Analyfica1 Chemistry.5th ed.;John Wiley & Sons: New York, 1994. (31) Berman, R J., et al. Micr0chem.J. 1989, 39, 20. (32) Ruzicka,J.; Hansen, E. H. Flow Injection
Analysis, 2nd ed.; Wiley Interscience:New
York. 1988. (33) Taylor, R H.; Ruzicka,I.;Christian, G. D. Talanfa 1992.3.285. (34) Ruzicka. J.; Manhall. G. D. Anal. Chim. Ada 1990,237,329. (35) Girbeli, T.; Christian, G. D.; Ruzicka. I. Anal. Chem. 1991,63,2407.
Gary D.Christian, Divisiona6 Dean of Sciences in the College ofArts and Sciences, performs research in electroanalytical chemistry, atomic spectroscopy, process analysis, and FIA.Address correspondence about this utticle to him ut the Ofice of the Dean, DS65, College 0fArt.i and Sciences, Univem’ty of Washington, Seattle, W A 98195.
