Quantitative analytical chemistry measures known substances in a sample for quality control, while qualitative analytical chemistry identifies unknown substances. Organic analysis is complex and uses instrumental methods like gas-liquid chromatography and electrophoresis. Inorganic analysis applies to carbonless chemistry and uses modern instrumental methods like atomic absorption or atomic emission spectroscopy. TLC is a vital technique in the pharmaceutical industry.
Quantitative analytical chemistry ascertains the quantities of known substances in a sample. Such tests are routinely performed for quality control, such as the level of active ingredients in cold compresses. Qualitative analytical chemistry seeks to know, not how much, but what is present: the identities of unknown substances. These determinations are not always routine and can be quite complex. Physical and chemical characteristics are determined as quickly and economically as possible, using a combination of carefully chosen instrumental and wet test methods.
Qualitative analytical chemistry is most conveniently divided into two types: organic analysis and inorganic analysis. Analytical qualitative organic chemistry is the more complex of the two. There are millions of possible organic compounds, thousands of which are known and characterized. A typical organic molecular structure may incorporate aliphatic chains or rings, aromatic rings, ether bonds, heteroatoms, double and triple bonds plus alcohol, carbonyl and carboxyl functionalities. Instrumental methods of identification are essential and commonly include gas-liquid chromatography and electrophoresis, as well as infrared, ultraviolet and mass spectroscopy.
Analytical Qualitative Organic Chemistry is one of the most interesting and important courses taught in universities. It requires composite knowledge of a number of chemical reaction types as well as a general understanding of instrumentation and the ability to read spectra, including nuclear magnetic resonance spectra. Knowledge of chemical stability is essential, as some tests can damage or destroy a sample or present a safety risk. The course also demonstrates the student’s familiarity with important data sources, including Beilstein’s historically invaluable library of organic compounds and their derivatives, comprising thousands of entries. Beilstein is still a major asset.
The pharmaceutical industry is vitally dependent on a qualitative analytical organic chemistry technique known as thin layer chromatography (TLC). A dish, perhaps glass, has an even layer of absorbent material. Small droplets of sample material are placed at the top of a swashplate and separation is accomplished via a descending solvent phase. This technique requires only traces and does not need high temperatures that can damage heat-sensitive substances. The compounds separate as they travel into distinct bands, from which each can be recovered and quantitatively measured if desired.
Inorganic qualitative analytical chemistry mainly applies to carbonless chemistry, including metal, nonmetal, hydroxyl, carbonate, and hydrogen ions. Testing can begin with a simple flame test or a pH measurement or manual titration. Previously standard wet testing methods have largely been replaced by modern instrumental methods, such as atomic absorption or atomic emission spectroscopy. Complex determinations can employ X-ray crystallography, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Applications include environmental analysis and materials analysis.
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