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Analytical Chemistry is the branch of chemistry principally concerned
with determining the chemical composition of materials, which may be solids,
liquids, gases, pure elements, compounds, or complex mixtures. In addition,
chemical analysis can characterize materials but determining their molecular
structures and measuring such physical properties as pH, color, and solubility.
Wet analysis involves the studying of substances that have been submerged in a
solution and microanalysis uses substances in very small amounts.
Qualitative chemical analysis is used to detect and identify one or more
constituents of a sample. This process involves a wide variety of tests.
Ideally, the tests should be simple, direct, and easily performed with available
instruments and chemicals. Test results may be an instrument reading, and
observation of a physical property, or a chemical reaction. Reactions used in
qualitative analysis may attempt to cause a characteristic color, odor,
precipitate, or gas appear. Identification of an unknown substance is
accomplished when a known one is found with identical properties. If none is
found, the uknown substance must be a newly identified chemical. Tests should
not use up excessive amounts of a material to be identified. Most chemical
methods of qualitative analysis require a very small amount of the sample.
Advance instrumental techniques often use less than one millionth of a gram. An
example of this is mass spectrometry.
Quantitative chemical analysis is used to determine the amounts of
constituents. Most work in analytical chemistry is quantitative. It is also
the most difficult. In principle the analysis is simple. One measures the
amount of sample. In practice, however, the analysis is often complicated by
interferences among sample constituents and chemical separations are necessary
to isolate tthe analyte or remove interfering constituents.
The choice of method depends on a number of factors: Speed, Cost,
Accuracy, Convenience, Available equipment, Number of samples, Size of sample,
Nature of sample, and Expected concentration. Because these factors are
interrelated any final choice of analytical method involves compromises and it
is impossible to specify a single best method to carry out a given analysis in
all laboratories under all conditions. Since analyses are carried out under
small amounts one must be careful when dealing with heterogeneous materials.
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