analytical chemistry

Branch of chemistry that deals with the determination of the chemical composition of substances. Qualitative analysis determines the identities of the substances in a given sample; quantitative analysis determines how much of a particular substance is present.

Simple qualitative techniques exploit the specific, easily observable properties of elements or compounds - for example, the flame test makes use of the different flame colours produced by metal cations when their compounds are held in a hot flame. More sophisticated methods, such as those of spectroscopy, are required where substances are present in very low concentrations or where several substances have similar properties.

Most quantitative analyses involve initial stages in which the substance to be measured is extracted from the test sample, and purified. The final analytical stages (or ‘finishes’) may involve measurement of the substance's mass (gravimetry) or volume (volumetry, titrimetry), or a number of techniques initially developed for qualitative analysis, such as fluorescence and absorption spectroscopy, chromatography, electrophoresis, and polarography. Many modern methods enable quantification by means of a detecting device that is integrated into the extraction procedure (as in gas-liquid chromatography).