Chapter I Introduction C hemistry is the study of matter, including its composition structure, physical properties, and reactivity. There are many approaches to studying chemistry, but, for convenience, we traditionally divide it into five fields: organic, inorganic, physical, biochemical, and analytical. Although this division is historical and arbitrary, as witnessed by the current interest in interdisciplinary areas such as bioanalytical and organometallic chemistry, these five fields remain the simplest division spanning the discipline of chemistry Training in each of these fields provides a unique perspective to the study of chemistry. Undergraduate chemistry courses and textbooks are more than a collection of facts; they are a kind of apprenticeship. In keeping with this spirit, this text introduces the field of analytical chemistry and the unique perspectives that analytical chemists bring to the study of chemistry
Chapter 1 1 Introduction Chemistry is the study of matter, including its composition, structure, physical properties, and reactivity. There are many approaches to studying chemistry, but, for convenience, we traditionally divide it into five fields: organic, inorganic, physical, biochemical, and analytical. Although this division is historical and arbitrary, as witnessed by the current interest in interdisciplinary areas such as bioanalytical and organometallic chemistry, these five fields remain the simplest division spanning the discipline of chemistry. Training in each of these fields provides a unique perspective to the study of chemistry. Undergraduate chemistry courses and textbooks are more than a collection of facts; they are a kind of apprenticeship. In keeping with this spirit, this text introduces the field of analytical chemistry and the unique perspectives that analytical chemists bring to the study of chemistry. 1400-CH01 9/9/99 2:20 PM Page 1
Modern Analytical Chemistry IA What is Analytical Chemistry? Analytical chemistry is what analytical chemists do We begin this section with a deceptively simple question. What is analytical chem istry? Like all fields of chemistry, analytical chemistry is too broad and active a disci pline for us to easily or completely define in an introductory textbook. Instead,we will try to say a little about what analytical chemistry is, as well as a little about what analytical chemistry is not. Analytical chemistry is often described as the area of chemistry responsible for haracterizing the composition of matter, both qualitatively(what is present)and quantitatively(how much is present). This description is misleading. After all, al most all chemists routinely make qualitative or quantitative measurements. The ar- gument has been made that analytical chemistry is not a separate branch of chem istry, but simply the application of chemical knowledge. In fact, you probably hav performed quantitative and qualitative analyses in other chemistry courses. For ex- ample, many introductory courses in chemistry include qualitative schemes for identifying inorganic ions and quantitative analyses involving titrations Unfortunately, this description ignores the unique perspective that analytical chemists bring to the study of chemistry. The craft of analytical chemistry is not in performing a routine analysis on a routine sample(which is more appropriately called chemical analysis), but in improving established methods, extending existing methods to new types of samples, and developing new methods for measuring chemical phenomena. by comparing the cost of removing the ore with the value of its contents. To esti- mate its value they analyze a sample of the ore. The challenge of developing and val idating the method providing this information is the analytical chemist,s responsi- bility. Once developed, the routine, daily application of the method becomes the job of the chemical analyst. Another distinction between analytical chemistry and chemical analysis is that analytical chemists work to improve established methods. For example, sev- plicate the quantitative analysis of Ni2+ in ores, including the presence of a complex heterogeneous mixture of silicates and oxides, the low con- centration of Niz+ in ores, and the presence of other metals that may interfere in the analysis. Figure 1. I is a schematic outline of one standard method in use dur ing the late nineteenth century. After dissolving a sample of the ore in a mixture of H2SO4 and HNO3, trace metals that interfere with the analysis, such as Pb2+, Cu2+ and Fet, are removed by precipitation. Any cobalt and nickel in the sample are reduced to Co and Ni, isolated by filtration and weighed (point A).After dissolving the mixed solid, Co is isolated and weighed(point B). The amount of nickel in the ore sample is determined from the difference in the masses at points A and B mass point A -mass point B mass sample
2 Modern Analytical Chemistry *Attributed to C. N. Reilley (1925–1981) on receipt of the 1965 Fisher Award in Analytical Chemistry. Reilley, who was a professor of chemistry at the University of North Carolina at Chapel Hill, was one of the most influential analytical chemists of the last half of the twentieth century. 1A What Is Analytical Chemistry? “Analytical chemistry is what analytical chemists do.”* We begin this section with a deceptively simple question. What is analytical chemistry? Like all fields of chemistry, analytical chemistry is too broad and active a discipline for us to easily or completely define in an introductory textbook. Instead, we will try to say a little about what analytical chemistry is, as well as a little about what analytical chemistry is not. Analytical chemistry is often described as the area of chemistry responsible for characterizing the composition of matter, both qualitatively (what is present) and quantitatively (how much is present). This description is misleading. After all, almost all chemists routinely make qualitative or quantitative measurements. The argument has been made that analytical chemistry is not a separate branch of chemistry, but simply the application of chemical knowledge.1 In fact, you probably have performed quantitative and qualitative analyses in other chemistry courses. For example, many introductory courses in chemistry include qualitative schemes for identifying inorganic ions and quantitative analyses involving titrations. Unfortunately, this description ignores the unique perspective that analytical chemists bring to the study of chemistry. The craft of analytical chemistry is not in performing a routine analysis on a routine sample (which is more appropriately called chemical analysis), but in improving established methods, extending existing methods to new types of samples, and developing new methods for measuring chemical phenomena.2 Here’s one example of this distinction between analytical chemistry and chemical analysis. Mining engineers evaluate the economic feasibility of extracting an ore by comparing the cost of removing the ore with the value of its contents. To estimate its value they analyze a sample of the ore. The challenge of developing and validating the method providing this information is the analytical chemist’s responsibility. Once developed, the routine, daily application of the method becomes the job of the chemical analyst. Another distinction between analytical chemistry and chemical analysis is that analytical chemists work to improve established methods. For example, several factors complicate the quantitative analysis of Ni2+ in ores, including the presence of a complex heterogeneous mixture of silicates and oxides, the low concentration of Ni2+ in ores, and the presence of other metals that may interfere in the analysis. Figure 1.1 is a schematic outline of one standard method in use during the late nineteenth century.3 After dissolving a sample of the ore in a mixture of H2SO4 and HNO3, trace metals that interfere with the analysis, such as Pb2+, Cu2+ and Fe3+, are removed by precipitation. Any cobalt and nickel in the sample are reduced to Co and Ni, isolated by filtration and weighed (point A). After dissolving the mixed solid, Co is isolated and weighed (point B). The amount of nickel in the ore sample is determined from the difference in the masses at points A and B. %Ni = mass point A – mass point B mass sample × 100 1400-CH01 9/9/99 2:20 PM Page 2
Chapter 1 Introduction Original Sample 1:3H2SO/HNO3100C(8-10h dilute Fe+ Co cool, add NH3 digest50-70°,30mn 应 Ca2+N|2+ slightly acidify w Hc heat, bubble H?s (g) ferric bubble H2s(g) add Na CO3 untl alkaline NaoH Co(OH)2. Ni(OH)2 Solution digest 24 h H2O, HCI Analytical scheme outlined by Fresenius for the gravimetric analysis of Ni in ores
Chapter 1 Introduction 3 Original Sample PbSO4 Sand Basic ferric acetate CuS 1:3 H2SO4/HNO3 100°C (8–10 h) dilute w/H2O, digest 2–4 h Cu2+, Fe3+ Co2+, Ni2+ Fe3+, Co2+, Ni2+ Fe(OH)3 CoS, NiS CuS, PbS Co(OH)2, Ni(OH)2 CoO, NiO cool, add NH3 digest 50°–70°, 30 min Co2+, Ni2+ Fe3+ Waste Waste Co2+, Ni2+ aqua regia heat, add HCl until strongly acidic bubble H2S (g) Co2+ Waste Solid Key Solution H2O, HCl heat add Na2CO3 until alkaline NaOH K3Co(NO3)5 Ni2+ neutralize w/ NH3 Na2CO3, CH3COOH slightly acidify w/ HCl heat, bubble H2S (g) HCl heat Co as above Co, Ni heat, H2 (g) HNO3 K2CO3, KNO3 CH3COOH digest 24 h dilute bubble H2S(g) A B Figure 1.1 Analytical scheme outlined by Fresenius3 for the gravimetric analysis of Ni in ores. 1400-CH01 9/9/99 2:20 PM Page 3
Modern Analytical Chemistry Original sam HNO,. HCL. heat Residue Solution 10% tartaric acid take alkaline with 1: 1 NH3 Yes take acid with Hc Solution take alkaline with 1: 1 NH3 Figure 1.2 Ni(DMG)2(s) Analytical scheme outlined by Hillebrand and Lundell for the gravimetric analysis of Ni 031 in the equation for %Ni accounts for 。Aono he difference in the formula weights of massA x g sample 100 Ni(DMG) and Ni; see Chapter 8 for more The combination of determining the mass of Ni by difference, coupled with the ed for many reactions and filtrations makes this procedure both time-consuming nd difficult to perform accurately The development, in 1905, of dimethylgloxime(DMG), a reagent that selec tively precipitates Ni2+ and Pd2+, led to an improved analytical method for deter mining Niz+ in ores. As shown in Figure 1. 2, the mass of Niz+ is measured directly, requiring fewer manipulations and less time. By the 1970s, the standard method for the analysis of Nit in ores progressed from precipitating Ni(DMG)2 to flame atomic absorption spectrophotometry, resulting in an even more rapid analysis Current interest is directed toward using inductively coupled plasmas for determ ing trace metals in ores. In summary, a more appropriate description of analytical chemistry is science of inventing and applying the concepts, principles, and measuring the characteristics of chemical systems and species. "6 Analytical chemists typically operate at the extreme edges of analysis, extending and improving the abil ty of all chemists to make meaningful measurements on smaller samples, on more complex samples, on shorter time scales, and on species present at lower concentra- tions. Throughout its history, analytical chemistry has provided many of the tools and methods necessary for research in the other four traditional areas of chemistry, as well as fostering multidisciplinary research in, to name a few, medicinal chem istry, clinical chemistry, toxicology, forensic chemistry, material science, geochem istry, and environmental chemistry
The combination of determining the mass of Ni2+ by difference, coupled with the need for many reactions and filtrations makes this procedure both time-consuming and difficult to perform accurately. The development, in 1905, of dimethylgloxime (DMG), a reagent that selectively precipitates Ni2+ and Pd2+, led to an improved analytical method for determining Ni2+ in ores.4 As shown in Figure 1.2, the mass of Ni2+ is measured directly, requiring fewer manipulations and less time. By the 1970s, the standard method for the analysis of Ni2+ in ores progressed from precipitating Ni(DMG)2 to flame atomic absorption spectrophotometry,5 resulting in an even more rapid analysis. Current interest is directed toward using inductively coupled plasmas for determining trace metals in ores. In summary, a more appropriate description of analytical chemistry is “. . . the science of inventing and applying the concepts, principles, and . . . strategies for measuring the characteristics of chemical systems and species.”6 Analytical chemists typically operate at the extreme edges of analysis, extending and improving the ability of all chemists to make meaningful measurements on smaller samples, on more complex samples, on shorter time scales, and on species present at lower concentrations. Throughout its history, analytical chemistry has provided many of the tools and methods necessary for research in the other four traditional areas of chemistry, as well as fostering multidisciplinary research in, to name a few, medicinal chemistry, clinical chemistry, toxicology, forensic chemistry, material science, geochemistry, and environmental chemistry. 4 Modern Analytical Chemistry Original sample Residue Ni(DMG)2(s) HNO3, HCl, heat Solution Solid Key Solution 20% NH4Cl 10% tartaric acid take alkaline with 1:1 NH3 Yes No A take acid with HCl 1% alcoholic DMG take alkaline with 1:1 NH3 take acid with HCl 10% tartaric acid take alkaline with 1:1 NH3 Is solid present? %Ni = × 100 mass A × 0.2031 g sample Figure 1.2 Analytical scheme outlined by Hillebrand and Lundell4 for the gravimetric analysis of Ni in ores (DMG = dimethylgloxime). The factor of 0.2031 in the equation for %Ni accounts for the difference in the formula weights of Ni(DMG)2 and Ni; see Chapter 8 for more details. 1400-CH01 9/9/99 2:20 PM Page 4
Chapter 1 Introduction You will come across numerous examples of qualitative and quantitative meth- ods in this text, most of which are routine examples of chemical analysis. It is im portant to remember, however, that nonroutine problems prompted analytical hemists to develop these methods. Whenever possible, we will try to place these methods in their appropriate historical context. In addition, examples of current re search problems in analytical chemistry are scattered throughout the text. The next time you are in the library, look through a recent issue of an analyti- ally oriented journal, such as Analytical Chemistry. Focus on the titles and abstracts of the research articles. Although you will not recognize all the terms and methods, you will begin to answer for yourself the question "What is analytical chemistry? IB The Analytical Perspective Having noted that each field of chemistry brings a unique perspective to the study of chemistry, we now ask a second deceptively simple question. What is the " analyt ical perspective"? Many analytical chemists describe this perspective as an analytical of the analytical approach as there are analytical chemists, it is convenient toro, g. approach to solving problems. Although there are probably as many description purposes to treat it as a five-step process: 1. Identify and define the problem. 2. Design the cedure 3. Conduct an experiment, and gather data 4. Analyze the experimental data. 5. Propose a solution to the problem. Figure 1.3 shows an outline of the analytical approach along with some im- portant considerations at each step. Three general features of this approach de serve attention. First, steps I and 5 provide opportunities for analytical chemists to collaborate with individuals outside the realm of analytical chemistry. In fact, many problems on which analytical chemists work originate in other fields. Sec ond, the analytical approach is not linear, but incorporates a"feedback loop consisting of steps 2, 3, and 4, in which the outcome of one step may cause a reevaluation of the other two steps. Finally, the solution to one problem often uggests a new problem Analytical chemistry begins with a problem, examples of which include evalu ating the amount of dust and soil ingested by children as an indicator of environ- mental exposure to particulate based pollutants, resolving contradictory evidence regarding the toxicity of perfluoro polymers during combustion, or developing rapid and sensitive detectors for chemical warfare agents. At this point the analyti cal approach involves a collaboration between the analytical chemist and the indi viduals responsible for the problem. Together they decide what information is needed. It is also necessary for the analytical chemist to understand how the prob- lem relates to broader research goals. The type of information needed and the prob- lem's context are essential to designing an appropriate experimental procedure. Designing an experimental procedure involves selecting an appropriate method of analysis based on established criteria, such as accuracy, precision, sensitivity, and detection limit; the urgency with which results are needed; the cost of a single analy- sis; the number of samples to be analyzed; and the amount of sample available for "These examples are taken from a series of articles, entitled the "Analytical Approach, which has appeared as a regular
Chapter 1 Introduction 5 You will come across numerous examples of qualitative and quantitative methods in this text, most of which are routine examples of chemical analysis. It is important to remember, however, that nonroutine problems prompted analytical chemists to develop these methods. Whenever possible, we will try to place these methods in their appropriate historical context. In addition, examples of current research problems in analytical chemistry are scattered throughout the text. The next time you are in the library, look through a recent issue of an analytically oriented journal, such as Analytical Chemistry. Focus on the titles and abstracts of the research articles. Although you will not recognize all the terms and methods, you will begin to answer for yourself the question “What is analytical chemistry”? 1B The Analytical Perspective Having noted that each field of chemistry brings a unique perspective to the study of chemistry, we now ask a second deceptively simple question. What is the “analytical perspective”? Many analytical chemists describe this perspective as an analytical approach to solving problems.7 Although there are probably as many descriptions of the analytical approach as there are analytical chemists, it is convenient for our purposes to treat it as a five-step process: 1. Identify and define the problem. 2. Design the experimental procedure. 3. Conduct an experiment, and gather data. 4. Analyze the experimental data. 5. Propose a solution to the problem. Figure 1.3 shows an outline of the analytical approach along with some important considerations at each step. Three general features of this approach deserve attention. First, steps 1 and 5 provide opportunities for analytical chemists to collaborate with individuals outside the realm of analytical chemistry. In fact, many problems on which analytical chemists work originate in other fields. Second, the analytical approach is not linear, but incorporates a “feedback loop” consisting of steps 2, 3, and 4, in which the outcome of one step may cause a reevaluation of the other two steps. Finally, the solution to one problem often suggests a new problem. Analytical chemistry begins with a problem, examples of which include evaluating the amount of dust and soil ingested by children as an indicator of environmental exposure to particulate based pollutants, resolving contradictory evidence regarding the toxicity of perfluoro polymers during combustion, or developing rapid and sensitive detectors for chemical warfare agents.* At this point the analytical approach involves a collaboration between the analytical chemist and the individuals responsible for the problem. Together they decide what information is needed. It is also necessary for the analytical chemist to understand how the problem relates to broader research goals. The type of information needed and the problem’s context are essential to designing an appropriate experimental procedure. Designing an experimental procedure involves selecting an appropriate method of analysis based on established criteria, such as accuracy, precision, sensitivity, and detection limit; the urgency with which results are needed; the cost of a single analysis; the number of samples to be analyzed; and the amount of sample available for *These examples are taken from a series of articles, entitled the “Analytical Approach,” which has appeared as a regular feature in the journal Analytical Chemistry since 1974. 1400-CH01 9/9/99 2:20 PM Page 5