Classical analysis. A look at the past, present, and ... - ACS Publications

A Lookat t&

Tmt, !Present, and !Fiuture espite the fact that instrumental analysis has rightfully assumed an overwhelmingly major role in the analytical laboratory, there remains a limited, although important, need for classical analysis. Instrumental analysis is most useful for elemental determinations at minor and trace levels (about 1% all the way down to 1atom), and in this range classical analysis performs either poorly or not at all. However, instrumental analysis generally does not give high precision and accuracy at major levels (about 1%up to loo%), and in this range classical analysis does perform well. Moreover, instrumental and classical analysis complement each other and can be used in tandem to the analyst’s advantage. In addition, classi-

Although classical analysis has taken a back seat to instrumental analysis since the 1940s, its revival is vital to the interests of industry Charles M. Beck II National Institute of Standards and Technology

224 A Analytical Chemistry, Vol. 66, No. 4, February 15, 1994

cal analysis will always be needed in order to establish standards for instrumental calibration. The purpose of this article is to define and discuss the scope of classical analysis and to explore the importance of renewing the chemical community’s interest in it. The histories of gravimetry and titrimetry are traced, including biographical sketches of some important personalities in the development of classical analysis in Europe and the United States. The significance of the events surrounding the Karl9 ruhe Congress of 1860 and the importance of physical chemistry and organic reagents to the development of classical analysis are discussed. The current crisis in the United States resulting from a This article not subject to US. copyright. Published 1994 American Chemical Society.

development and general use of classical ing current conditions and needs and for analysis and the beginning of instrumenanticipating future possibilities. tal analysis. Although the use of instrumental analysis had been growing slowly History of gravimetry to the up until that time, most samples were ana- i850s lyzed classically. Since the 1940s instruGravimetry is the determination of an elemental analysis has assumed more impor- ment through the measurement of the tance because of the ever-increasing weight of an insoluble product of a definite chemical reaction involving that ele demands for sensitivity, speed, and economy. @or a sketch of the history of instrument. Tracing the history of gravimetry mental analysis, see Reference 1.) amounts to tracing the early history of What is classical analysis? chemistry. Chemistry is at least as old as After World War 11, the existing,unIf the final step of an analysis is a gravirecorded history, but what we recognize derutilized instrumentation, as well as metric or titrimetric determination, it is subsequently developed instrumentation, as experimental chemistry did not emerge considered a classical analysis. The foluntil the end of the sixteenth century. was made practical with the introduction lowing test may be useful in distinguishof the photomultiplier tube, the transistor, Later, with the publication of his book ne ing classical from instrumental analyses. Sceflticul Chymist in 1661, Robert Boyle and the microprocessor. We now have The calculations for a classical analysis began the process of putting chemistry on require no more than experimentally mea- sensitivitiesand speeds that would have been unimaginable even a few years ago, a sound scientific footing. Boyle firmly sured weights (or weights and volumes), dismissed Aristotle’s four elements of fire, but, as has always been the case, new dedefinite chemical reactions, and atomic air, water, and earth and Paracelsus’ three mands keep pushing the definitions of weights. Such a test demonstrates, for principles of mercury, sulfur, and salt. “fast” and “ultratrace”to new levels. example, that a potentiometric titration is Instead, he advocated a comprehensive Because many, if not most, analytical a classical analysis, because the potentiexperimental approach before attempting chemists in the work force today were ometer serves only to indicate the endeducated after the beginning of the instru- any theoretical statements. point of the titration. It also demonstrates As the influence of Paracelsus waned, mental era in the 1950s, it is useful to rethat a spectrophotometric determination interest in chemistry shifted from mediview the history of classical analysis. An is an instrumental analysis because the cine to mineralogy and metallurgy. Howawareness of the history of a discipline calculations require an experimentally measured transmittance of light through a helps to provide a perspective for evaluat- ever, chemists were influenced for another century by the “phlogiston theory,” solution. first advocated in 1681by Johann Becher There are two good reasons for clearly and popularized by Georg Ernst Stahl. distinguishing between a classical and an According to this theory, when a metal instrumental analysis. First, in the hands burns or rusts it gives off a substance of an experienced analyst, the relative p r e called phlogiston. When the phlogistoncision of a classical analysis is about 0.1%ists observed that iron gained weight 0.2% or better, whereas the relative preciwhen it rusted, they simply postulated sion of an instrumental analysis is about that phlogiston had negative weight. As 1%-2%(although certain exceptions exdamaging as this theory was to the ist), Second, whereas almost all instruprogress of chemistry, it did provide a mental analyses are comparative and regeneral concept, and testing that concept quire known standards for calibration, led to a study of chemical analysis and classical analyses do not require external simple chemical reactions. standards for calibration if the stoichiome Among those making such studies tries implied by the written chemical reacwere the gas chemists Joseph Black, tions reflect what is actually happening in Henry Cavendish, Carl Scheele, Daniel the analytical process. For gravimetry this Rutherford, and Joseph Priestley. Alimplies that actual precipitatescorrespond though Priestleywas one of the last to written formulas, and for titrimetry that staunch defenders of the phlogiston t h e actual reactions correspond to written ory, he initiated its downfall in 1774when reactions and that indicators detect true he isolated a gas by heating mercuric oxequivalence points. ide in a closed system. He gave the name We have advanced far enough beyond “dephlogisticated air” to the oxygen he the 1940s to see that that decade was a collected. A few years earlier, Rutherford watershed period marking the end of the

shortage of qualified classical analysts is examined. The future use of classical and instrumental analysis in tandem is examined. Because of the serious economic consequences to American industry and government that would result from the disappearance of classical analysis, a proposal is made for the renewal of education in this field.

Chmistry is at bast as old as recorded history, but

what we recognize as

everimental

dkmiktry did’ not emerge until th endofthe

si@eenth century.

Analytical Chemistry, Vol. 66, No. 4, February 15, 1994 225 A

and Cavendish had independently discovered nitrogen, which Rutherford called “phlogisticated air.” Aware of Rutherford’s and Priestley’s work, Antoine Laurent Lavoisier dealt the death blow to the phlogiston theory by performing quantitative experiments with mercury and air in a closed system. He correctly explained combustion and demonstrated that air was a mixture of nitrogen and oxygen. His genius, his instinctive recognition of the law of conservation of mass, and his use of the balance made him the forefather of the quantitative era in chemistry. At about the same time, the Swedish chemist Torbem Bergman outlined a systematic scheme of qualitative and quantitative analysis and described all of the available known reagents. His gravimetric method for silica is recognizable as a direct forerunner of the one we use today. Strangely enough, Bergman remained a fmn believer in the phlogiston theory all his life. Although titrimetry already was being used in France at the tum of the nineteenth century, almost all analyses were done by gravimetry. For example, Sismund Andreas Mar& had worked out the determination of silver as silver chloride as a substitute method for fire assay which, under certain conditions, tended to give low results for silver. (Fire assay is the ancient art of isolating precious metals from an ore. The method is based on a high-temperature liquid-liquid extraction in which the ore is fused with a mixture of lead oxide, flux,and a reducing agent. Molten lead is formed throughout as the mixture is heated and the precious metals pass into the lead. Upon cooling, a lead “button”forms at the bottom of the mass from which the precious metals can be extracted.) Bergman was already using gravimetric factors to calculate the amounts of iron, lead, copper, and silver in various precipitates, and others were b e coming interested in the analysis of minerals and industrial materials. At the turn of the nineteenth century chemistry entered a period of great confusion. Gravimetry had been developing through the eighteenth century in an empirical manner, because the laws of chemical composition were not understood. Many chemists believed that substances combined in definite proportions. For ex-

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ample, they knew that a certain weight of silver always gave the same weight of silver chloride. Jeremias Benjamin Richter, a mining engineer in Silesia, also believed that there was an equivalence inherent in chemical reactions. He tried to work out the mathematical relationships and coined the word “stoichiometry”for the proportions existing among various substances. Unfortunately, he was led down many a blind path because he tried to force his data to fit his preconceptions. His work was a step in the right direction, however, because he had an intuitive sense of the law of definite composition. Such was not the case with the famous French chemist Claude Louis Berthollet, who wrongly postulated that the composition of a compound of two elements might vary between maximum and minimum in all proportions. Joseph Louis Proust o p posed Berthollet’s view and presented experimental evidence that metals form oxides and sulfides of definite composition. He also recognized that if a metal forms two oxides, each has a definite composition and no product of an intermediate composition exists. With this observation he came close to discovering the law of multiple proportions. In 1808John Dalton published the first part of the book New S’ysfem of ChemicaE PhiZuso$hy. He proposed the idea that matter was composed of small discrete particles. Although this concept dated back to


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the Greeks of 400 B.C., Dalton’s theory was much more far-reaching;it explained the law of conservation of mass as well as the laws of definite composition and multiple proportions. Dalton realized that b e cause compounds are formed by uniting atoms of different elements with different relative weights that can be expressed numerically, the composition of chemical compounds can be expressed quantitatively. He constructed a table of atomic weights, but because of his poor data he was unable to demonstrate the simple relationships that intuitively he knew must exist. Also in 1808Joseph Louis Gay-Lussac published a paper on the combining volumes of gases. He consistently found that the volume ratios in gaseous reactions were small whole numbers. This result seemed to contradict Dalton’s atomic t h e ory because if one volume of C1 and one volume of H gave two volumes of HC1, then the “atoms”of C1 and H must divide-a logical impossibility if the atomic theory were true. Amedeo Avogadro reconciled the dilemma in 1811by assuming that equal volumes of gases under the same conditions contained the same number of particles, which he called “molecules.” He reasoned that these gaseous molecules split into “half-molecules”when they react. In effect, he supposed that elemental gases contained more than one atom, but he

never used the term atom. Dalton refused to accept Gay-Lussac’slaw and thus could not appreciate Avogadro’s remarkable and revolutionary insight. We know today that Avogadro’s reasoning was correct, but the chemists of his day either rejected or simply ignored his hypothesis. Efforts in 1814 by Andre Marie Ampkre and in 1826 by Jean Bap tiste Dumas to revive Avogadro’s hypothe sis went unnoticed. The world of chemis try was not ready for Avogadro. Sadly, it would take another 50 years of confusion about atomic weights before Stanislao Cannizzaro would successfully revive Avogadro’s hypothesis. During this period of confusion, practical analysts with little interest in theoretical matters were doing very accurate gravimetric analyses of metals, minerals, and water. Among these were Richard Kerwan, who published an outstanding book listing all the references on water analysis since the lime of Bergman; Martin Heinrich Klaproth, who discovered many elements in his analyses of minerals; and Louis Nicolas Vauquelin, who was widely known for his pure reagents. The dominant figure of this period was Jons Jakob Berzelius. During an extraordinarily productive decade between 1807 and 1818, he devised the system of chemical symbols and notations we use today and, through a series of elegant analyses, determined the atomic weight of many of the elements. Unfortunately, he also d e vised his dualistic theory, which p r e vented him from accepting Avogadro’s hypothesis. Nevertheless, his analytical expertise was nothing short of incredible, and the atomic weights published in his 1828 table approach today’s values, if you discount the fact that a few of the ele ments listed were twice their correct values. Working with the equipment of his day, much of which he improved himself, Berzelius produced a quantity of accurate work that would be a credit to a modern, wellequipped research laboratory. Although Berzelius was one of the world’s greatest analysts,it is doubtful that he ever viewed himself as such. In contrast, Karl Remegius Fresenius thought of himself as an analyst from the beginning of his remarkable career. After being an apprentice pharmacist in Frankfurtfor severalyears, he took courses at

the university‘in Bonn and worked in the private laboratory of Carl Marguart, his professor of pharmacy. Working mostly alone and without instruction,Fresenius taught himself and kept good notes. Marguart was so impressed with these notes that he suggested they be published. Anleitung zur qualitativen chemischen Analyse, published in 1841, was an immediate success and was to see 16 editions under Fresenius’ authorship. The 17th edition, overseen by his son, was translated by C. A. Mitchell in 1921 as Introduction to Qualitative Chemical Analysis. Fresenius went to the University of Giessen as a lecturer, worked in Liebig’s laboratory,and obtained his Ph.D. in 1842, using his new book-already in its second edition-as his thesis.

as Quantitative Chemical Analysis. Fresenius’ small house/laboratory would grow to become the worldrenowned Fresenius Institute. By 1855 his laboratory had 60 students, all of whom were e k b l e to receive university credit for the time they spent there. In addition to providing instruction,the institute rap idly became known throughout government, industry, and academia as an analytical laboratory. In 1862 Fresenius founded Zeitschriftfir analytische Chemie, the first journal entirely devoted to analytical chemistry. His influence throughout Europe and the entire world was enormous. History of titrimetry to the 1850s

Titrimetry is the determination of an element through the measurement of the weight of a chemical necessary to just complete a definite chemical reaction in a solution containing that element. The weight of the chemical is usually obtained indirectly by measuring the volume of a standard solution of that chemical, although for very accurate work the amount of standard solution needed can be measured by weighing it. Industry‘s need for rapid methods for determining acids, alkalis, carbonates, and hypochlorites provided the driving force for the development of titrimetry. Early development was confined almost solely to France, where it was crudely practiced in the eighteenth century. Endpoints were determined by the “clear point,” the cessation of effervescence, or the use of a few plantextsact indicators. Francois Antoine Henri Descroizilles devised a method for determining the hyHe was hired in 1845 as professor of chemistry, physics, and technology at the pochlorite strength of bleaching solution used in the textile industry. He first added Agricultural College at Wiesbaden. B e a measured amount of dilute sulfuric acid cause the college administrators repeatedly refused to supply funds for a chemis- containing an indigo indicator to a graduated cylinder and then slowly added the try laboratory,he borrowed money from hypochlorite solution (whose strength his father, a prosperous attorney, bought was being tested) until the color changed a house, and remodeled it into a private analytical laboratory. He opened the doors from blue to pale green. He then read the volume from the graduations on the side in 1848 with five students and one assistant, Emil Erlenmeyer. Only 30 years old, of the cylinder. Descroizilles later devised a method for determining the alkaline Fresenius was already an experienced strength of potash. He used a graduated analyst. Shortly after assuming his duties buret filled with dilute sulfuric acid and at Wiesbaden, he published his second controlled the flow by covering a small air book, Anleitung zur quantitativen chemishole in the top with his h g e r . chen Analyse, which ran to six editions Gay-Lussac’s contributions to titrime and was translated in 1904by A. I. Cohn

Industry’s need for rapid

deteminiy acid$ aliuLii, carbonates, andhypodilbrites provided the d k v i yf o r e for the develbpment of tit7i”J.

Analytical ChemistryJVol. 66, No. 4, February 15, 1994 227 A

try and the widespread use of his methods helped establish titrimetry as part of classical analysis. He improved Descroizilles’ method for potash and made several improvements in the hypochlorite method, notably the introduction of the redox indicator. As an analyst, Gay-Lussac is most famous for the silver assay method named after him. The French government, which was losing money because of errors in the fire assay of silver, asked Gay-Lussac in 1829to devise a rapid and simple method with a relative error of 0.05%.He made a 1WmL pipet that would deliver repeatedly with very high precision, and he p r e pared a standard chloride solution that he adjusted so that the delivery of the pipet was equivalent to Loo00 g of Ag. He then dissolved a bullion sample expected to contain just over 1g of Ag and added one pipet full of the standard solution. After vigorous agitation, the silver chloride p r e cipitate was allowed to flocculate and settle to the bottom of the flask. Using a 1:lO dilution of the standard chloride solution, he continued the titration in 1-mLincrements until no more turbidity was produced in the supernatant. He achieved a relative accuracy and precision better than the requested 0.05%,and to this day no improvements on this assay method have been made except for the use of a potentiometric endpoint for deeply colored solutionsor alloys of silver containing tin. From 1835to about 1855 many different titrimetric methods were developed but not widely used. As a result of GayLussac’s work, however, titrimetry b e came known outside of France, especially in Germany and England. It was not yet possible to establish a general system of titrimetrybecause the concentrations of standard solutionshad no chemical basis; there were no unique atomic weights and stoichiometry was not understood. Houton de la Billardibre discovered the usefulness of iodine in titrimetry in 1826, and in 1853Robert Wilhelm Bunsen published an excellent paper on iodimetry describing the determination of more than 20 elements. In that same year, Karl Leonhard Heinrich made a great advance by recommending the use of sodium thiosulfate for titrating iodine. Nevertheless, the famous analysts of the period remained

1 contemptuous of titrimetry. Berzelius never used it, and Fresenius recommended that it not be used for important analyses. Karl Friedrich Mohr did much to overcome the difficulties of titrimetry. He studied under the direction of Heinrich Rose and Leopold Gmelin, Bunsen’s predecessor at Heidelberg. Mohr took over his father’s pharmacy in 1830 and in his spare time experimented with various titrimetric methods. Because he remained outside academia, he was never regarded as a scientist in Germany, but his contributions to titrimetry were many. He introduced the use of potassium chromate as an internal indicator for chloride determination (Mohr meqod), oxalic acid as a primary standard for alkalimetry, ferrous ammonium sulfate (Mohr’s salt) as a standard for oxidizing agents, and the.idea of back titration. As for laboratory equip ment, he invented the cork borer, the Liebig condenser, the Mohr pinch-cock, the pinchcock buret, and calibrated pipets. After his book Lehrbuch der chemkchanalytkchen Titrirmethode was published in two parts in 1855 and 1856, titrimetric analysis became widely known in Europe. The publication of Mohr‘s books marked the end of the early history of titrimetry, although in 1883Johan Gustaf C. T. Kjeldahl developed his well-known method for the determination of nitrogen. He discovered that sulfuric acid could be used to digest organic materials, converting free ammonia and “organicallybound” nitrogen to ammonium sulfate. After add-

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ing excess strong caustic, he distilled the liberated ammonia into a known excess of standard sulfuricacid and determined the unreacted acid by a back titration. The method has remained unchanged, except for the use of various catalysts to aid in the digestion and Lauos Winkler‘s discovery that the distilled ammonia can be a b sorbed into a boric acid solution and titrated directly with standard acid. Winkler contributed more than 200 original papers on gravimetry and titrimetry and is probably best remembered for his titrimetric method for the determination of dissolved oxygen in water (published in 1888). The Karlsruhe Congress of 1860

By the late 1850s classical analysis had come about as far as it could without a consistent table of atomic weights. Atomic weight tables varied among different countries and sometimes among different laboratorieswithin the same country. To resolve this problem, Friedrich August Kekulk-with the help of Charles Adolphe Wurtz and Carl Weltzien-invited dele gates to an internationalcongress at Karlsruhe, Germany, in 1860.About 140 of the world’s leading chemists attended. Cannizzaro, a young professor at the University of Genoa, who for some time had realized the value of Avogadro’s hypothesis in resolving the problems surrounding atomic weights, addressed the Karlsruhe Congress with great passion and pedagogical skill. He showed how Avogadro’s hypothesis could be used to

establish the molecular weight of a gas and demonstrated that by comparing the vapor densities of a series of gaseous compounds of a particular element, the molecular weight and atomic weight of that element could be determined. Although Cannizzaro pleaded with his colleagues for the adoption of atomic weights based on Avogadro’s hypothesis, he was unable to sway congress members in his favor. The congress adjourned, having reached no agreement on atomic weights, but it was in adjourning that the key event of the congress occurred. As the delegates departed, Cannizzaro’s colleague, Angel0 Pavesi from the University of Pavia, passed out reprints of Cannizzaro’s 1858 publication, Sunto di un con0 di Filosofi chimica (Sketch of a Course of Chemical Htilosoply) .This paper set forth clearly what Cannizzaro had been teaching his students at Genoa Although his paper had gone largely unnoticed in the literature, it did not go unnoticed in the hands of the delegates. Julius Lothar Meyer read it twice on his homeward journey. Everything became clear to him, as if scales fell from his eyes. Dmitrii Ivanovitch Mendeleev later said that even though no agreement was reached by the congress, the truth of the law of Avogadro as advocated by Cannizzaro soon convinced everyone. Without the insight that both Meyer and Mendeleev gained from Cannizzaro’s paper, it is doubtful that they independently would have gone on to work out the periodic table in 1869. It is hard to overestimate the impact of the events surrounding the Karlsruhe Congress. The confusion over atomic weights almost completely disappeared in just a few years, and analysts were able to write down correct stoichiometric formulas for their precipitates. Gravimetry was placed on solid, although still somewhat empirical, ground. Titrimetry also benefited from this great advance, but it (and, to a lesser extent, gravimetry) lacked a firm scientificbasis until the development of physical chemistry at the end of the nineteenth century. Gravimetry comes to the United States In the mid-nineteenthcentury almost all new developments in chemistry were tak-

ing place in Europe. Graduate schools did not develop in the United States until near the end of the century. From about the middle of the century, Germany was the place to go for graduate education in chemistry. Justus Liebig, who established a teaching laboratory at the University of Giessen, generated remarkable enthusiasm and camaraderie among his students, and his laboratory became a model for other graduate programs and teaching laboratories throughout Germany.

to give chemistry a try. He entered the University of Heidelberg in 1872 and studied under the guidance of Bunsen and Gustav Kirchhoff, earning his Ph.D. in 1875. He stayed on at Heidelberg for another year of research and then spent three semesterswith Rudolph Fittig at Strasbourg. Realizing that organic chemistry did not appeal to him, he decided to finish his studies at the mining academy at Freiberg to supplement the training in mineral analysis, which he received under the direction of Bunsen. He had made up his mind to become an analytical chemist. He returned to the United States in 1878 and, failing to find immediate work in the East, made his way in 1879 to Leadville, CO, where he became the thiid partner in a small assaying h. Samuel F. Emmons, an occasional customer who was in charge of the Rocky Mountain Division of the newly formed United States Geological Survey (USGS),offered Hillebrand a job as a chemist. Hillebrand considered Emmons’ offer the opportunity of a lifetime and quickly accepted. He remained in the Denver laboratory of the USGS until 1885, when he was transferred to the Washington USGS laboratory to work under the direction of the chief chemist, Frank W. Clarke. Hillebrand’s careful work set a new standard of excellence in the analysis of rocks and ores. During his 29 years at the USGS, he made more than 400 complete analyses of silicate rocks. The signiicance William Francis Hillebrand was born in of his work lay in the perfection of a separation scheme for materials as complex as Honolulu seven years before the Karlscarbonate and silicate rocks. Even in the ruhe Congress, and his story is perhaps the best example of how classical analysis, late nineteenth century, the problem wasn’t so much the lack of a suitable particularly gravimetry, was brought to the United States. His father, a Germanmethod for the final determination of an born medical doctor, established a pracelement as it was the lack of suitable sepatice in Hawaii because its climate would ration methods preceding the final deterhelp him to recover from a serious illness. mination-a problem that still exists. Because his father intended to return to In 1897 Hillebrand wrote a 5Gpage Germany with the entire family,Hilleintroduction to USGS Bulletin No. 148on the methods of analysis of silicate rocks, brand was sent to Comell in 1870 to preand this was quickly translated into Gerpare for study at a German university. The family moved to Bonn in the sum- man. In 1900 the introduction was revised, mer of 1872, and Hillebrand had to choose enlarged, and printed as an independent document, Bulletin No. 176. The next edia career. He had no interest in medicine and felt he lacked the mental qualification appeared in 1907 as Bulletin No. 305. tions for law or engineering. His father It included carbonate rocks and was also suggested chemistry. Remembering with translated into German. The series culmipleasure his study of the basics of chemis- nated in 1919 with the well-known Bulletin try back in Honolulu, Hdebrand decided No. 700, a book of 285 pages.

workhy in tfie pefection of a separation schemefor m a t e r i d as wmpli. as car6onate and s i l i t e rocks.


tury.Agreat breakthrough was made be-

Hillebrand was unquestionably one of the world’s leading analysts when he was called to be chief chemist at the National Bureau of Standards (NBS) in 1909. Administrative duties in his new position limited his time at the bench, but the steady stream of books and papers continued. He greatly contributed to the increase of the standard samples program at NBS, expanding it from a few cast irons to more than 60 materials. (Today, the Standard Reference Materials Program at the National Institute of Standards and Technology [NIST, formerly NBS] has more than 1200 standard reference mate rials available, covering a broad range of materials that are certified for chemical composition and/or physical property.) Hillebrand had a talent for gathering around him capable people, and his success in bringing Gustaf E. F. Lundell from Comell in 1917 is a good example. In 1923 he and Lundell began co-authorship of Applied Inotganic Analysis. Hillebrand died in 1925 before the work was completed, but by 1929 Lundell had finished the book, which became known as the “analyst’sbible.” Together with James I. Hoffman, Lundell wrote a companion volume in 1938, Outlines of Methods of Chemiwhich became another clascal Anal’, sic. (Hoffman and Hany A Bright brought out a second edition of Applied Inotganic Analysis in 1953.) Lundell was appointed chief chemist at NBS in 1937, and under his leadership the

scope and renown of its efforts in chemical analysis grew. He had a talent for picking the right person for a particular assignment, and he had an almost uncanny ability to sense whether work on a project that had hit a snag should be stopped or continued. Often his timely encouragement resulted in the solution of a seemingly hopeless problem. In 1933 Lundell published his well-known paper, “The Chemical Analysis of Things as They Are” (2).The continuing relevance of his insights is remarkable, and this paper should be required reading for all analytical chemists. Physical chemistry applied to classical analysis

Once the confusion over atomic weights was settled, the stage was set for the maturation of gravimetry. Although many refinements would result from the application of physical chemistry to gravimetry, putting it to practical use did not require an understanding of the rate of precipitate formation, growth of crystalline precipitates, adsorption and occlusion of impurities, and the aging of precipitates. Such was not the case with titrimetry. Correct atomic weights certainly were as necessary for titrimetry as for gravimetry. However, input from the newly emerging physical chemistry would be essential for titrimetry to reach maturity. Physical chemistry did not emerge until the last third of the nineteenth cen-

230 A Analytical Chemistryl Vol. 661No. 4, February 15, 1994

tween 1864 and 1879when the Norwegian brothers-in-law Cat0 M. Guldberg and Peter Waage formulated the law of mass action. In 1884 Jacobus Henricus van’t Hoff made an elegant derivation of the law of mass action based on thermodynamics. His clear and inspiring treatment of chemical dynamics brought the entire subject of reaction kinetics and equilibria before the chemical world. Certain anomalies that occurred when the laws of physical chemistry were applied to solutions of electrolytes were explained in 1887 when the revolutionary theory of electrolytic dissociation was published by Svante August Arrhenius. It was Wilhelm Ostwald who recognized the importance of the work done by van’t Hoff and Arrhenius. Through his books, research, and personal contacts, Ostwald was influential in spreading the ideas of the new physical chemistry. With van’t Hoff he founded the journal Zeitschrifrf i r physikalische Chemie in 1887, and he championed the cause of physical chemistry as a science in its own right. In essence, he “organized” physical chemistry at the end of the nineteenth century. In 1894 Ostwald published Die urissenschaftlichen Crrrdagm der analMchen Chemie (The Sdmt@c Foundatiom of Analytical Chemistry) and thereby began to put classical analysis on a scientitic basis. In the preface he noted that although the technique of chemical analysis stood at a very high level, its scientifictreatment was almost completely neglected. Ostwald’s book was a significant start toward correcting this deficiency. He discussed precipitation in detail, including the increase in particle size of standing crystalline precipitates-a process that became known as “Ostwald ripening.” The most important part of the book dealt with chemical separations. By combining the law of mass action and Arrhenius’ theory of electrolytic dissociation,he introduced the concepts of dissociation constants and solubility product constants. Although Ostwald’s little book broke new ground and was soon recognized as a classic, it suffered some significant omissions. For example, the phase rule of Josiah Willard Gibbs was not mentioned. Perhaps Ostwald was simply unaware of Gibbs’ work because it had been pub

lished in a rather obscure journal. However, it is difficult to understand why he made no mention of the work of Walter Nernst, who originated the famous Nernst equation while working in Ostwald’s own laboratory in 1889. Nernst explored many analytical applications of his equation, and he is rightly considered the father of modern electroanalytical chemistry. Titrimetry comes to the United States

As was the case with gravimetry, titrime try developed in Europe and then came to the United States, chiefly through the efforts of Izaak Maurits Kolthoff, who came to the University of Utrecht in Holland in 1911. Kolthoff ’s lack of certain prerequisites demanded by the chemistry department was a blessing in disguise because it brought him under the tutelage of Nicolaas Schoorl in the school of pharmacy. Schoorl had studied under the direction of van’t Hoff and was aware of the recent advances in physical chemistry. He imme diately recognized Kolthoffs talent and encouraged him to carry out independent research. Kolthoff had trouble understanding the proper selection of indicatorsfor acidbase titrations and therefore launched his own investigation. He had already acquired a used copy of Ostwald’s 1894 classic, and he was further encouraged by the 1909paper of the Danish physiological chemist S.P.L. SBrensen, who introduced the concept of pH. Kolthoff was further inspired in 1913by the work of Joel Hilde brand, who used the hydrogen reference electrode in electrometric titrations. Kolthoff borrowed pH measuring equip ment, but within a year he had devised his own potentiometric apparatus. In 1915he published his first paper on the titration of phosphoric acid. Kolthoff quickly realiied the importance of physical chemistry to analytical chemistry, but in those early years, some times the going was rough. Not recognizing the significance of his early work, chemistry department faculty members sometimes criticized him. Some went so far as to try to block him from publishing and lecturing. Despite such criticism, Kolthoff forged ahead and in 1918presented his Ph.D. thesis on the “Fundamentals of Iodimetry,” a topic he returned

to again and again over the years. In 1914 the Danish physical chemist Niels J. Bjerrum published a book showing how to calculate both the shape of neutraliiation curves and the titration errors in visual endpoint determinations. Bjerrum’s work inspired Kolthoff to d e velop a theoretical interpretation of all the methods of titrimetry. (This work resulted in his famous two-volume book, fist pub lished in German in 1926 and translated in 1928 and 1929 as VolumetricAnalysis by N. Howell Furman of Princeton University. A three-volume revision of the work appeared between 1942 and 1957.)

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required radittyfor

In 1924 Kolthoff conducted a lecture tour of Canada and the United States, where he met both Furman and Hobart H. Willard of the University of Michigan. Willard had pioneered precipitation from homogeneous solution and also investigated the analytical uses of perchloric acid. Furman made outstanding contributions in potentiometry, electrodeposition, and polarography, and together with Willard worked on the analytical applications of ceric salts. In addition to becoming good friends, these men became “The Big Three” in graduate education in analytical chemistry in this country. In 1927 Kolthoff accepted a professorship at the University of Minnesota and continued his monumental achievements, which touched almost every area of analytical chemistry. Between 1932 and 1960 these three men supervised 120 Ph.D.s in analytical chemistry. Their educational progeny are into the

third and fourth generations and number in the thousands. Kolthoff also has influenced many thousands of undergraduate students through his well-known Textbook of Quantitative Inorganic Analysis, coauthored with Ernest B. Sandell in 1936.A fourth edition appeared in 1969with Sandell, Edward J. Meehan, and Stanley Bruckenstein as co-authors and now that it is out of print, it is particularly treasured by those in the field of analytical chemistry who own a copy. Organic reagents applied to classical analysis

Classical analysis does not suffer from a lack of good analytical methods for the final gravimetric or titrimetric determination of an element, provided that the ele ment occurs alone. But because this is never the case, interferingelements must be removed. The elaborate scheme perfected by Hillebrand for the analysis of rocks is an example of a general separation scheme built on the experience of generations of analysts. Based almost entirely on precipitation separations using inorganic reagents, it stands as one of the monumental achievements of classical analytical chemistry. Beginning in the last century and extending up to the 1940s,various organic reagents were introduced that could be used as precipitants in gravimetric determinations. They were extremely useful b e cause they were selective for a very few elements and could be used to determine one of those elements when others were absent or had been removed. Most of these organic reagents were chelating agents such as dmethylglyoxime and a-benzoin oxime, used for the determination of nickel and molybdenum, respectively. In addition to being used as precipitants, these and other organic reagents were extremely useful when coupled with immiscible solvent extraction. This procedure can be used for the separation of aluminum in the widely used titanium alloy with nominal composition 6%Al, 4%V, and 0.2%Fe. Addition of cupferron to an acid solution of the alloy produces the insoluble cupferrates of titanium, vanadium, and iron. Extraction of the solution with chloroform leaves aluminum in the aqueous phase ready for determination by titrimetry or gravimetry.


r

In the 1930s it was discovered that certain amino polycarboxylic acids formed stable, soluble complexes with many metals, and in the 1940s Gerold Schwarzenbach began a theoretical examination of the complexes. This work led to the development of the titration of calcium and magnesium with EDTA and the introduction of metallochromic indicators. Schwarzenbach’s work made an extraordinary contribution to titrimetry, and thousands of papers have appeared on EDTA-related methods. Ionexchange resins are perhaps the most significant contribution to classical analysis resulting from the use of organic reagents. Ion exchange had been o b served in certain natural materials in the middle of the nineteenth century, but these materials were unstable in acidic and alkaline solutions. In 1934 two British chemists, B. A. Adams and E. L. Holmes, discovered the cation-exchange properties of a synthetic organic polymer made from formaldehyde and tannic acid. Later, crosslinked polystyrene resins with ionizable acidic or basic functional groups were synthesized, and these could exchange with cations or anions. Great advances in the understanding and use of ionexchange resins occurred during World War I1 because of the research performed in conjunction with the Manhattan Project. In 1942 George E. Boyd and his group used ion-exchange resins to separate plutonium from uranium. Later Boyd and his associates used ion exchange to separate the elements produced in fission prior to chemical analysis. Meanwhile, Frank H. Speddmg and his group at Ames, IA, performed largescale separations of naturally occurring rare-earth elements. Because of the secrecy surrounding the Manhattan Project, none of this work was announced until after the conclusion of the war. Since that time, many ionexchange separation procedures have been developed and there is extensive literature on the subject. The equipment for ion exchange is relatively simple but, unlike immiscible solvent extraction,ionexchange separations are time consuming. When one considers their usefulness, however, they are worth the investment of time. For example, manganese, iron, cobalt, nickel, cop

per, and zinc in strong hydrochloric acid can be completely separated on an anionexchange column using successive elutions with hydrochloric acid of different concentrations (3). This ionexchange system has greatly simpmed the assay for zinc in zinc ore concentrates. After dissolving the ore concentrate in acid and volatiliziigarsenic, antimony, and tin as their bromides, the solution is placed on an anion-exchange column where all remaining interfering elements (except cadmium) can be separated by elution with 0.5 M HC1. Zinc and cadmium are eluted with 0.005 M HCl, and the zinc is determined by EDTA titrimetry after the cadmium is masked as its iodide complex.

17ie analysis SCht?llZ

for roks i s built on the e?cperienceof JeneratiOns of ana@sts. The immense power of ion exchange is further illustrated by the complete separation of the common rock-forming elements (except silicon and phosphorus) using a single cationexchange column (4). After acid dissolution of the rock sample and volatilization of SiF,, the solution is placed on a cationexchange column and, by using a series of eluants, vanadium, sodium, potassium, titanium, zirconium, iron, manganese, magnesium, calcium, and aluminum are eluted in order. Although the procedure is slow, taking two &h days, the separations are complete and the recoveries compare well with those of traditional classical separation methods. The present

Although classical analysis will never be used to the extent that it was in the past, it will continue to be essential. However, the current situation in the United States is


critical; a recent review article (5)states that The last two years have shown a continued accelerationof the trend away from classical ‘wet chemical’techniquesin favor of highspeed, low overhead instrumentation.With the exception of a few techniques based on fundamental approaches, these high-speed instruments are dependent upon comparative methodology that requires calibration and validation with traceable standard reference materials. The loss of experience and knowledge in the area of classical analytical chemistry upon which so many of the extant reference materials are based remains a crisis of growing proportions. Nowhere is this trend greater than in the U.S. where the classical wet chemical laboratory is vanishing from the steel industry.

As an illustration of the current need for classical analysis in industry, consider my experiences over the past seven years. While working for a large corporation engaged in advanced ceramic research, workers at our laboratory were asked to assay each of the elements (except oxygen) in the following compounds: Sic, Tic, WC, BN, AlN, Si,N,, TiN, A1203, SiO,, ?ioa,and Y203. In most cases the required relative precision and accuracy was 0.5%or better, and in many cases mixtures of two or more of the compounds were submitted for analysis. While working for a major forging company, we were asked to assay aluminum-,titanium-, and nickel-based alloys for Al, V, Mo, Cr, Co, Zn, and Sn in the 5%-60% range with a r e quired relative precision and accuracy of 0.2%or better. All of these requests finally arrived at the classical analyst’s bench because instrumental methods failed to provide the needed precision and accuracy. Without exception each of the assays was of considerable economic importance to the industries involved. Even though such critical needs exist, only a minimal amount of classical analysis is being taught at colleges and universities. Although a few exceptional schools may offer more, most cover only one or two gravimetric determinations and three or four titrimetric determinations. To some degree, this is understandable. Colleges and universitiesresponded to the explosive growth of instrumental analysis by changing their curricula. Having more material to cover in four years, professors

had to sacrifice something, and traditional qualitative and quantitative analysis were among the casualties. The analytical chemistry community allowed training in classicalanalysis to slip away until, by about the mid-l97Os, industrial, government, and private laboratories were having trouble finding qualified classical analysts. As the shortage intensified, laboratoriesbegan providing on-the-jobtraining, but eventually their experienced classicalanalystswho were doing the training retired. The final phase in the decline came when young would-be classical analysts tried to learn from the old texts and reference works, only to find most of them out of print. The unavailability of these books remains a serious problem for anyone wanting to study classical analysis. Wishing for them to be reprinted would be to ignore the economic realities of publishers. However, some way must be found to preserve and make available the informa-

tion they contain. Attempts to revise these old reference books would be a disaster, because the methods they contain are of great value and often can provide the basis for elegant reconstructions when combined with instrumental techniques. Classical and instrumental analyses in tandem

Classical analysts have been combining classical and instrumental methods for many years in individual situations.However, two papers by Silve Kallmann that appeared in the mid-1980s advocated a conscious, systematic approach to using classical and instrumental analysis in concert (6, 7). Often, older classical analyses can be reconstructed and revitalized by using them together with instrumental determinations. Sometimes entirely new methods, some of which are very elegant, are possible. He suggests that the classical analyst continually consider such pos sibilities as a part of the overall analytical

approach to methods development. There are at least two opportunities for combining instrumental determinations with gravimetry. The first is checking the purity of precipitates. Despite the fact that every effort is made to choose optimum conditions for precipitation, many precipitates are significantly contaminated with coprecipitated elements. Such an impure precipitate can be redissolved and the contaminant(s) determined by instrumental analysis. The second area is checking the filtrate from a gravimetric determination for solubility product effects. No gravimetric precipitate is completely insoluble, but the filtrate can be examined by instrumental analysis for the small amount of unprecipitated element. For example, the classical method for silica can be simplified greatly by isolating the precipitated silica from a single dehydration and then determining the remainder in the filtrate instrumentally. IWImann points out other examples

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of how a method that may have been rejected because of a slightly soluble precip itate can now be reconstructed. There are also opportunities for comb i n i i instrumental determinations with titrimetry. In the zinc assay of a zinc ore concentrate cited earlier, the small amount of cadmium present in all zinc ores is eluted together with the zinc. The cadmium can be separated from the zinc, but that requires either using a second ionexchange column or masking the cadmium through its iodide complex. The easiest way to solve this problem is to titrate the zinc and cadmium together and determine the cadmium separately by atomic absorption spectroscopy. The foregoing examples will not pass the test for a classical analysis proposed at the beginning of this article, but the purpose of the test is to exclude methods with relative precisions poorer than about 0.1%-0.2%.The use of an instrumental determination together with a classical

determination does not degrade the overall precision as long as the instrumental method is used to determine a very small part of the total. In addition, the accuracy of gravimetric determinations is increased by reducing the biases of coprecipitation and solubility product effects. Revitalizing education for classical analysts

We have seen that classical analysis has a long and distinguished history. The last 100 years have witnessed a strange reversal in classical analysis. The analysts at the end of the nineteenth century, for the most part, had excellent technique even though their scientiticunderstanding was very limited. Through the middle of the twentieth century, classical analysis had both good technique and good scient& understanding. Today's chemists have excellent understanding but almost no practical experience in classical analysis. This turnaround must be reversed or

there will be severe economic consequences for American industry.The following ad appeared in the catalog of a well-known analytical laboratory (8). For over two years . . . (we have) been providing sanctuary for members of an endangered species. Now, after proper care and nurturing,we are ready to reintroduce our specimens of this vanishing breed, so that they can provide services for the public. This creature to which we refer is the Ckrssical Analytical Chemist. He is the primary source of accurate analysis and is, therefore, extremely valuable to our industry.

It is doubtful that colleges and universities ever again will offer sufticient training to resupply the work force with well-trained classical analysts. Because of the fiercely competitive nature of research grant funding, few professors of classical analysis could long survive in a modern American chemistry department. How ironic that our situation bears some similarity to that of mid-nineteenth century Europe, which

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had few laboratorieswhere students could practice analysis. By the middle of the nineteenth century European colleges and universities were eager to equip analytical teaching laboratoriesbecause classical analysis was on the cutting edge of fundamental research. Elements remained to be discovered, and new minerals and rocks needed to be characterized.Teaching lab oratories for classical analysis are needed today, but for different reasons. Industry will continue to depend on the classical analyst to decide if raw materials meet specifications and if finished products should be released for sale. Classical analysis is essential in the development of new materials and in the production of the reference materials on which almost all instrumental methods depend. For years many laboratorieshave been looking for people to replace their retired classical analysts. Some analytical laboratories have given up the search. I specu-

instmmental methdijiaili.6 to Provide the needed precision and

accurucy. late that many hundreds, and perhaps as many as several thousand, well-trained classical analysts may be needed. If there were a recognized school where qualified

classical analysts were trained, recruiters would probably line up at the door at graduation time. Fresenius' laboratory was started with private funds in a converted house with one assistant and five students. In five years he had 30 students, and in eight years he had 60 students and a worldwide reputation. The same thing could happen today. With a few capable and dedicated teachers, a school with an excellent reputation could be established in less than a decade. Industry or a joint venture by industry and government would have to bear the cost, but further delay in addressing the problem would be more costly. Actually, such a venture would not require a huge investment. The building and equipment requirements for such a teaching laboratory would be relatively modest, but those in charge of the administration and instructionwould need to be people of great ability, experience, and commitment. They would also have to

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understand the correct pedagogical order. The traditional educational sequence of studying qualitative and quantitative analysis before physical chemistry must be avoided. Understanding the theory of gravimetry and titrimetry requires a knowledge of physical, inorganic, and organic chemistry,and all of these must be considered prerequisites. The science, art,and “state of mind” necessary for a good classical analyst would have to be firmly imparted to each student. Students would have to practice until they mastered the techniques of common classical analytical o p erations and would have to analyze materials used in industry and government to gain proper experience. From such a school could flow a small but steady stream of qualified classical analyststo serve in our industrial,government, and private laboratories.The graduates of this school would have the mental and manual skills necessary to do classi-

cal analyses. They would be able to work according to Kolthoff s maxim, “theory guides, experiment decides.” Perhaps such a school exists. If not, now is the time to establish one. For many helpful discussions and suggestions, the author is indebted to James R DeVoe, John C. Travis, Michael S. Epstein, Richard I. Martinez, Jerry D. Messman,John R Moody, Kenneth W. Pratt,Marc L Salit,Johanna M.B. Smeller, and ThomasW.Vetter of NIST; Karen D. Norlin, Wyman-GordonCo.; Donald L Dugger and William J. Rourke, GTE Laboratories, Inc.; Leo W. and Marjorie P. Ollila, hvak, Inc.; and James I. Shultz,ASTM.Adapted from Ana-

lytical Chemistry 1991,63(20),993A-1003A

References (1) Laitinen, H. A J Res.Nut. Bur. Stand. 1988,93,17M%. (2) Lundell, G.E.F. I d . Eng. Chem.Anal. Ed. 1933,5,221-25. (3) Kraus, K. A; Moore, G. E.J Am. Chem. SOC.1953,75,1460-62. (4) Strelow, F.W.E.; Liebenberg, C. J.; Vidor, A H.Anal. Chem. 1974,46,140%14. (5) Dulski, T. R Anal. Chem. 1991,63,65R (6) Kallmann, S. Anal. Chem. 1984,56,

1020A-1028 A (7) Kallmann, S. In ChemicalAnalysis of Metakr; Coyle, F. T.,Ed.; ASTM: Philadelphia, 1987;pp. 128-33. (8) B m m e r Standards Company, Inc. Catalog Supplement, 1988;p. 3.

Suggested reading Belcher, R Analyst, 1978,103,2%36. Some Fundamentals of Analytical Chemistry, Byme, F. P., Ed.; ASTM:Philadelphia, 1974. Cannizzaro, S. Sketch of a Course of Chemical Hzilosophy; Livingstone:Edinburgh (Alembic Club Reprint #18), 1969. Chmside, R C. Analyst, 1961,85,314-24. deMilt, C.J Chem. Educ. 1951,28,421-25. Fiidlay, A A Hundred Years of Chemistry,3rd ed.; revised by Williams, T. I.; Duckworth: London, 1965. Hamilton, L F.; Simpson, S. G. Calculations of Analytical Chemistry, 7th ed.; McGraw Hilk New York, 1969. Hillebrand, W. F.J. Znd. Ew. Chem. 1917,9, 17&77. Hillebrand, W. F.; Lundell, G.E.F.; Bright, H. A; Hoffman, J. I. Applied Inorganic Analy sk,2nd ed.;Wiley: New York, 1953. Ihde, A J. m e Development of Modem chemist7>); Harper & Row: New York, 1964. Kodama, IC Methods of Quantitative Inorganic Analysis; Interscience: New York, 1963.

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Kolthoff, I. M.; Stenger, V. A; Belcher, R; Matsuyama, G. VolumetricAnalysis; Interscience: New York, 1942,1947,1957 (3 vols.). Kolthoff, I. M.; Sandell, E. B.; Meehan, E. J.; Bruckenstein, S. Quantitative Chemical Analysis, 4th ed.; Macmillan: New York, 1969. Kolthoff, I. M. Anal. Chem. 1973,45,24A37 A. A History ofAnalytica1 Chemistry; Laitinen, H. A; Ewing, G. W., Eds.; The Division of Analytical Chemistry of the American Chemical Society: Washington, DC, 1977. Lundell, G.E.F.; Hoffman,J. I.; Bright, H. A. ChemicalAnalysis of Iron and Steel; Wiley: New York, 1931. Lundell, G.E.F.; Hoffman,J. I. Outlines of Mefhods of Chemical Analysis; Wiley: New York, 1938. Meinke, W. W. Anal. Chem. 1970,42,26A38 k Partington, J. R A History of Chemistry;Macmillan: New York, 1961,1962,1964 (3 vols.).

Standard Methods of Chemical Analysis, The Elements, 6th ed.; Furman, N. H., Ed.; Krieger: New York, 1975. Szabadvhry,F. History of Analytical Chemistry; Pergamon Press: New York, 1966. Szabadvhry,F.; Robinson, A. In Comprehensive Analytical Chemistry;Svehla, G., Ed.; Elsevier: New York, 1980;Vol. 10. Treadwell, F. P.; Hall, W. T. Analytical Chemist v , 9th ed.; Wiley: New York, 1942;Vol. 2. Washington, H. S. The Chemical Analysis of Rocks, 4th ed.; Wiley: New York, 1930. Wilson, H. N. Analyst, 1960,85,540-50. Wilson, H. N. An Approach to Chemical Ana& siS; Pergamon: New York, 1966.

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Charles M. Beck II is a research chemist in the Chemical Science and Technology Lube ratory, Inorganic Analytical Research Division at the National Institute of Standards and Technology, Gaithenburg, M D 20899. He received his B. S. degree from Worcester Polytechnic Institute in 1963 and has worked as an analytical chemist in government, private, and industrial analytical laboratories. Before joining NIST in 1990, he was senior chemist at Wyman-Gordon Co., Eastern Division, Worcester, MA. His research interests are in the areas of sample preparation, chemical separations, classical elemental determinations, cert$cation of standard reference materials for chemical composition, and the history of analytical chemistry.

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New in this edition are a section on determining detection limits, the general elimination of boiling point and density specifications, the use of LC in assay determinations, and a section on preparation of volumetric solutions. Twenty-four new reagents have been added. Updated methods include gas chromatography where capillary columns are now used, water determinations where coulometric methods have been added, and the replacement of flame emission techniques by atomic absorption for metal determinations. In addition, the general methods for chromatography and atomic absorption have been extensively revised t o reflect their practical use in today’s typical analytical laboratory. 815 pages (1993) Clothbound ISBN 0-8412-2502-8 $149.95 American Chemical Society Distribution Office Dept. 51 1155Sixteenth Street, NW Washington, DC 20036 Or CALL TOLL FREE

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