Analytical chemistry is a branch of chemistry that deals with the development and use of techniques for chemical measurement. Chemists use those techniques to determine the chemical composition of substances. Chemical analysis may be qualitative or quantitative. Qualitative analysis identifies the elements or compounds that make up substances. Quantitative analysis measures the amounts of some or all of the elements or compounds.
Early analytical chemists obtained information that led to our modern understanding of matter. For example, Theodore W. Richards developed analytical techniques that accurately determined the relative atomic masses of many chemical elements. In 1914, Richards became the first American scientist to win the Nobel Prize in chemistry (see Richards, Theodore William ).
Chemists use the techniques of analytical chemistry to test a sample of a substance. Some methods involve chemical reactions that are characteristic of a known substance. If the substance being analyzed undergoes those reactions, then that substance may be the known substance. Other techniques measure the substance’s absorption of light. Still others measure the light emitted (given off) by the substance. Related methods measure the absorption and emission of other forms of electromagnetic radiation, such as ultraviolet rays and infrared rays (see Spectroscopy ). Chemists use electroanalysis to observe how a sample responds to electric signals. Mass spectrometry enables researchers to identify compounds by measuring the mass (amount of matter) of the different parts of a molecule (see Mass spectrometry ).
Chemists may separate complex substances, such as body fluids and industrial chemicals, into their components before analyzing them. Methods of separation include chromatography and extraction (see Chromatography ).
Analytical chemistry provides important information for science and industry. For example, chemical analysis is used to test samples of air, soil, and water to identify pollutants. Medical technicians use analytical methods to help in the diagnosis of disease. Raw materials and products in the food, drug, and other industries are analyzed in quality control tests. Modern forensic laboratories use analytical techniques to examine evidence connected with a crime (see Forensic science ).
