QUANTITATIVE CHEMICAL ANALYSIS

branch of chemistry that deals with the determination of the amount or percentage of one or more constituents of a sample. A variety of methods is employed for quantitative analyses, which for convenience may be broadly classified as chemical or physical, depending upon which properties are utilized. Chemical methods depend upon such reactions as precipitation, neutralization, oxidation, or, in general, the formation of a new compound. The major types of strictly chemical methods are known as gravimetric analysis (q.v.) and volumetric, or titrimetric, analysis (see volumetric analysis). Physical methods involve the measurement of some physical property such as density, refractive index, absorption or polarization of light, electromotive force, magnetic susceptibility, and numerous others. An analysis will often require a combination of methods: qualitative for separating desired constituents from a sample and quantitative for measuring the amounts present. The basic tool in all quantitative analyses is the analytical balance, used for the accurate weighing of samples and precipitates. For usual analytical work the balance should be able to determine differences in mass of 0.1 milligram (about 0.000004 ounce). In microanalyses the balance must be about 1,000 times more sensitive, and, for special work, balances of even higher sensitivity have been constructed.