chemical analysis, the study of the chemical composition and structure of substances. More broadly, it may be considered the corpus of all techniques whereby any exact chemical information is obtained. There are two branches in analytical chemistry: qualitative analysis and quantitative analysis. Qualitative analysis is the determination of those elements and compounds that are present in a sample of unknown material. Quantitative analysis is the determination of the amount by weight of each element or compound present. The procedures by which these aims may be achieved include testing for the chemical reaction of a putative constituent with an admixed reagent or for some well-defined physical property of the putative constituent. Classical methods include use of the analytical balance, gas manometer, buret, and visual inspection of color change. Gas and paper chromatography are particularly important modern methods. Physical techniques such as use of the mass spectrometer are also employed. For samples in the gaseous state, optical spectroscopy provides the best technique for determining which atomic and molecular species are present.