Qualitative and quantitative analysis
Like most forms of analysis, it can be broken down into two main categories. Qualitative analysis reveals the chemical identity of the species in the sample based on its qualities. Quantitative analysis establishes the relative amount of one or more of these species, or analytes, in numerical terms. Qualitative information is required before a quantitative analysis can be undertaken. A separation step is usually a necessary part of both a qualitative and a quantitative analysis.
Role of analytical chemistry in the sciences
Analytical chemistry has played a vital role in the development of science. For example, in 1894 Wilhelm Ostwald wrote:
Analytical chemistry, or the art of recognizing different substances and determining their constituents, takes a prominent position among the applications of science, since the questions which it enables us to answer arise wherever chemical processes are employed for scientific or technical purposes. Its supreme importance has caused it to be assiduously cultivated from a very early period in the history of chemistry, and its records comprise a large part of the quantitative work which is spread over the whole domain of science.
Since Ostwald’s time, analytical chemistry has evolved from an art into a science with applications throughout industry, medicine, and all the sciences. To illustrate, consider a few examples. The amounts of hydrocarbons, nitrogen oxides, and carbon monoxide present in automobile exhaust gases must be measured in order to determine the effectiveness of smog-control devices. Quantitative measurements of ionized calcium in blood serum help diagnose parathyroid disease in human patients. The quantitative determination of nitrogen in foods establishes their protein content and thus their nutritional value. Analysis of steel during its production permits adjustment in the concentrations of such elements as carbon, nickel, and chromium to achieve a desired strength, hardness, corrosion resistance, and ductility. The mercaptan content of household gas supplies is monitored continually to assure that the gas has a sufficiently obnoxious odor to warn of dangerous leaks. Modern farmers tailor fertilization and irrigation schedules to meet changing plant needs during the growing season. They gauge these needs from quantitative analyses of the plants and the soil in which they grow.