Quantitative Vs. Qualitative
The general expression Qualitative Analysis refers to analyses in which substances are identified or classified on the basis of their chemical or physical properties, such as chemical reactivity, solubility, molecular weight, melting point, radiative properties (emission, absorption), mass spectra, nuclear half-life, etc. Quantitative Analysis refers to analyses in which the amount or concentration of an analyte may be determined (estimated) and expressed as a numerical value in appropriate units. Qualitative Analysis may take place without Quantitative Analysis, but Quantitative Analysis requires the identification (qualification) of the analyte for which numerical estimates are given.
— International Union of Pure and Applied Chemistry, Nomenclature in evaluation of analytical methods including detection and quantification capabilities, Pure & Appl. Chem. 67(10), p. 1701 (1995)
The term "quantitative analysis" is often used in comparison (or contrast) with "qualitative analysis", which seeks information about the identity or form of substance present. For instance, a chemist might be given an unknown solid sample. He or she will use "qualitative" techniques (perhaps NMR or IR spectroscopy) to identify the compounds present, and then quantitative techniques to determine the amount of each compound in the sample. Careful procedures for recognizing the presence of different metal ions have been developed, although they have largely been replaced by modern instruments; these are collectively known as qualitative inorganic analysis. Similar tests for identifying organic compounds (by testing for different functional groups) are also known.
Many techniques can be used for either qualitative or quantitative measurements. For instance, suppose an indicator solution changes color in the presence of a metal ion. It could be used as a qualitative test: does the indicator solution change color when a drop of sample is added? It could also be used as a quantitative test, by studying the colour of the indicator solution with different concentrations of the metal ion. (This would probably be done using ultraviolet-visible spectroscopy.)
Read more about this topic: Quantitative Analysis (chemistry)
Famous quotes containing the word qualitative:
“You ask: What is it that philosophers have called qualitative states? I answer, only half in jest: As Louis Armstrong is said to have said when asked what jazz is, ‘If you got to ask, you ain’t never gonna get to know.’”
—Ned Block (b. 1942)