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...