1: Introduction
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Analytical chemistry is the science of how to make good measurements that we can use to solve a chemical problem. Many problems in analytical chemistry begin with the need to identify what is present in a sample. This is the scope of a qualitative analysis, examples of which include identifying the products of a chemical reaction, screening an athlete’s urine for a performance-enhancing drug, or determining the spatial distribution of Pb on the surface of an airborne particulate. An early challenge for analytical chemists was developing simple chemical tests to identify inorganic ions and organic functional groups. The classical laboratory courses in inorganic and organic qualitative analysis, still taught at some schools, are based on this work.
Perhaps the most common analytical problem is a quantitative analysis, examples of which include the elemental analysis of a newly synthesized compound, measuring the concentration of glucose in blood, or determining the difference between the bulk and the surface concentrations of Cr in steel. Much of the analytical work in clinical, pharmaceutical, environmental, and industrial labs involves developing new quantitative methods to detect trace amounts of chemical species in complex samples. Most of the examples in this text are of quantitative analyses.
Another important area of analytical chemistry, which receives more limited attention in this text, are methods for characterizing physical and chemical properties. The determination of chemical structure, particle size, and surface structure are examples of a characterization analysis.
The purpose of a qualitative, a quantitative, or a characterization analysis is to solve a problem associated with a particular sample. The purpose of a fundamental analysis, on the other hand, is to improve our understanding of the theory that supports an analytical method and to understand better an analytical method’s limitations.
Like all areas of chemistry, analytical chemistry is so broad in scope and so much in flux that it is difficult to find a simple definition more revealing than this quote attributed to C. N. Reilly (1925-1981), who was a professor of chemistry at the University of North Carolina at Chapel Hill and one of the most influential analytical chemists of the last half of the twentieth century:
"Analytical chemistry is what analytical chemists do."
In this chapter we expand upon this simple definition by introducing approaches to making analytical measurements and by developing a shared language for discussing analytical chemistry, more generally, and instrumentation, more specifically.
- 1.1: Classification of Analytical Methods
- Analytical methods often are divided into two classes: classical methods of analysis and instrumental methods of analysis.
- 1.2: Types of Instrumental Methods
- It is useful to organize instrumental methods of analysis into groups based on the chemical or physical properties that we use to generate a signal that we can measure and relate to the analyte of interest to us.
- 1.3: Instruments For Analysis
- The basic components of an instrument include a probe that interacts with the sample, an input transducer that converts the sample's chemical and/or physical properties into an electrical signal, a signal processor that converts the electrical signal into a form that an output transducer can convert into a numerical or visual output that we can understand. In this section we develop a common vocabulary that we can use in later chapters.
- 1.4: Selecting an Analytical Method
- Choosing an analytical method requires matching the method's strengths and weaknesses—its performance characteristics—to the needs of your analysis.
- 1.5: Calibration of Instrumental Methods
- To standardize an analytical methods we need to determine its sensitivity, which relates the signal to the analyte's concentration. There are three general calibration strategies that are outlined here: external standards, standard additions, and internal standards.