Major Categories of Chemical Analysis

Both qualitative and quantitative analyses are divided between classical methods involving primarily chemical reactions and simple measurements of mass and volume and instrumental methods that use instruments of varying degrees of complexity and sophistication to measure quantities of analytes. Classical methods are often wet chemical procedures using reagents in solution and reactions of dissolved analytes. Instrumental methods use various devices to measure physical manifestations of chemical species and chemical reactions, such as absorption of light, electrical potentials, or small changes in temperature. 

Analytical chemistry can also be divided between chemical and physical methods of analysis. Chemical methods almost always involve the measurement of a mass of a chemical species or a volume of a reagent solution produced or consumed by a chemical reaction. For example, the acid in an acid mine water sample can be determined by adding exactly enough of a solution of base (NaOH) of accurately known concentration to exactly neutralize the strong acid in the sample 

Physical methods of analysis normally involve a measurement of a physical parameter other than mass or volume. For example, a water sample suspected of being polluted with hexavalent chromium can be injected into an inductively coupled plasma atomic emission spectrometer (ICP/AES) and the intensity of light given off by the very hot chromium atoms emitted by the sample measured to give the chromium concentration. Or fluoride in a water sample can be determined by measuring the potential versus a reference electrode of a fluoride ion-selective electrode immersed in the sample and comparing that value with the potential measured in a standard F solution to give the value of [F ]. 

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