Common Analytical Problems

Common Analytical Problems

We indicated that analytical chemistry is more than a collection of qualitative and quantitative methods of analysis. Nevertheless, many problems on which analytical chemists work ultimately involve either a qualitative or quantita- tive measurement. Other problems may involve characterizing a sample’s chemical or physical properties. Finally, many analytical chemists engage in fundamental studies of analytical methods. In this section we briefly discuss each of these four areas of analysis.

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 the presence of a performance-enhancing drug, or determining the spatial dis- tribution of Pb on the surface of an airborne particulate. Much of the early work in analytical chemistry involved the development of simple chemical tests to identify the presence of inorganic ions and organic functional groups. The classical labora- tory courses in inorganic and organic qualitative analysis,9 still taught at some schools, are based on this work. Currently, most qualitative analyses use methods such as infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry. These qualitative applications of identifying organic and inorganic compounds are covered adequately elsewhere in the undergraduate curriculum and, so, will receive no further consideration in this text.

Perhaps the most common type of problem encountered in the analytical lab is a quantitative analysis. Examples of typical quantitative analyses include the ele- mental analysis of a newly synthesized compound, measuring the concentration of glucose in blood, or determining the difference between the bulk and surface con- centrations of Cr in steel. Much of the analytical work in clinical, pharmaceutical, environmental, and industrial labs involves developing new methods for determin- ing the concentration of targeted species in complex samples. Most of the examples in this text come from the area of quantitative analysis.

Another important area of analytical chemistry, which receives some attention in this text, is the development of new methods for characterizing physical and chemical properties. Determinations of chemical structure, equilibrium constants, particle size, and surface structure are examples of a characterization analysis.

The purpose of a qualitative, quantitative, and characterization analysis is to solve a problem associated with a sample. A fundamental analysis, on the other hand, is directed toward improving the experimental methods used in the other areas of analytical chemistry. Extending and improving the theory on which a method is based, studying a method’s limitations, and designing new and modify- ing old methods are examples of fundamental studies in analytical chemistry.