Analytical chemistry is the branch of science that determines the properties of chemical substances, as well as the structure and composition of compounds and mixtures. Much of the science of modern chemistry is built on results obtained from analyses. Important applications of chemistry that rely on analytical techniques range from solving a murder case to determining whether a river is polluted.
The primary aim of analysis is to find out how a material is constituted. A chemist analyzes a mixture to find out which compounds are present or analyzes a pure compound to identify the elements contained in it. All the structures of chemical compounds illustrated in this book were originally worked out by various types of analysis.
Chemical analysis helps maintain high quality-control standards for the products we eat, drink, and take to stay healthy. Chemicals are often added to foods as preservatives, colorants, or flavorings. Regular testing ensures that the proper additives are used in the correct quantities. Such testing requires analytical procedures of the utmost sensitivity, so food and drug analysis is a specialized field, often involving complex mixtures of natural products as well as synthetic compounds. Measuring the amounts of various additives is an important part of food analysis.
Diseases and other medical disorders lead to changes in the concentration and production of various chemicals in the body. An imbalance of any substance may indicate medical problems. Clinical analysis plays an important part in the diagnosis of medical conditions.
For example, simple chemical tests for glucose (sugar) in the blood or urine can reveal whether or not a person is diabetic. The demand for chemical analyses for medical purposes is now so great that automated methods are used whenever possible.
The detection of crime and the conviction of criminals is an area of growing importance in chemical analysis, in this field, known as forensic analysis, almost every analytical tool is called into play. For instance, to determine whether or not a fire has been started deliberately, ashes and debris are analyzed for the presence of kerosene, gasoline, or solvents. Analysis detects not only the material used to start the fire but also the identity of its individual components. And the conviction of drug dealers may depend on the correct identification of what may look like harmless white powder. Granulated sugar, talcum powder, and flour must be distinguished from morphine, heroin, and cocaine.
Chemical analysis is necessary to maintain the quality of most of the products we use. As chemicals are manufactured, their rate of production is often checked automatically by online analytical equipment. The final material also undergoes rigorous tests to ensure that it is the correct material and satisfies quality specifications. Minute amounts of unwanted impurities can cause it to be rejected. Quality control is vitally important with chemicals intended for human use, such as pharmaceuticals and cosmetics. Even household products such as polishes, bleaches, detergents, and paints all require analytical checks to ensure that the correct amounts of chemicals have been mixed and that the products are safe to use.
Many of the 109 known chemical elements were discovered through improvements in analytical techniques. The history of four relatively uncommon elements—yttrium, erbium, terbium, and ytterbium—is an interesting example. These elements derive their names from Ytterby, a town in Sweden. In the 1700’s, Finnish chemist Johan Gadolin identified what he thought was a new element in a mineral (gadolinite) that he discovered near Ytterby. The element, named yttrium, is one of a group called the rare earth elements (lanthanides) that have very similar chemical properties. As analytical techniques improved during the 1800’s, Gadolin’s yttrium was found to be a mixture of several elements. First, two other elements—erbium and terbium—were isolated from it Then these two were found to be mixtures of several elements. One of these elements was subsequently called ytterbium, thus commemoratinq Ytterby for the fourth time.
Analytical techniques are methods for finding out something specific about an element or compound. They are based on differences in the chemical and physical properties of mate
rials. Sometimes, these differences are very small, making analytical work difficult and often time-consuming. Refinements in this important set of analytical techniques—those that separate different compounds or elements— led to the isolation and identification of the full range of rare earth elements.
In the 1900’s, chemists developed ever more sensitive separation techniques. Often, as in the case of chromatographic methods, the techniques are rooted in the research of the 1800’s. We can now separate very small amounts of complex molecules from one another. Much of the recent progress in understanding the chemistry of biological processes has stemmed from the development of such techniques.
Analysis does not always depend on separation, however. One of the triumphs of modern analytical chemistry has been the development of a broad spectrum of techniques that can detect very small amounts of a particular substance in a complex mixture. Such techniques may be qualitative or quantitative. They may reveal only what material is there (quality), or they may also indicate how much of that material is present (quantity). For example, it is possible to detect very small concentrations of particular pollutants in the atmosphere. The atmosphere is a simple mixture of nitrogen and oxygen, gases that make up about 99 per cent of its total volume. The remaining 1 per cent is a complex mixture that makes quantitative analysis of trace substances a demanding task. Flowever, it can also be an essential one. The build-up of pollutants like chlorofluorocar-bons (CFC’s) could have a serious effect on world climate, making life more difficult than it already is.
Quantitative techniques, developed for measuring very small amounts of particular molecules, often depend on the physical rather than chemical behavior of the molecules— how they interact with different types of radiation, for example. A problem facing chemists in recent years is that the ability to measure very small amounts of different substances has surpassed the ability to understand the various effects of these substances. Thus, chemists can now measure unbelievably small concentrations of certain impurities in food but do not know whether they are harmless below a certain threshold level.