Analytical ChemistryAnalytical Chemistry is the branch of chemistry principally concernedwith 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 molecularstructures and measuring such physical properties as pH, color, and solubility. Wet analysis involves the studying of substances that have been submerged in asolution and microanalysis uses substances in very small amounts. Qualitative chemical analysis is used to detect and identify one or moreconstituents of a sample. This process involves a wide variety of tests. Ideally, the tests should be simple, direct, and easily performed with availableinstruments and chemicals.
Test results may be an instrument reading, andobservation of a physical property, or a chemical reaction. Reactions used inqualitative analysis may attempt to cause a characteristic color, odor,precipitate, or gas appear. Identification of an unknown substance isaccomplished when a known one is found with identical properties. If none isfound, the uknown substance must be a newly identified chemical.
Tests shouldnot use up excessive amounts of a material to be identified. Most chemicalmethods of qualitative analysis require a very small amount of the sample. Advance instrumental techniques often use less than one millionth of a gram. Anexample of this is mass spectrometry. Quantitative chemical analysis is used to determine the amounts ofconstituents. Most work in analytical chemistry is quantitative.
It is alsothe most difficult. In principle the analysis is simple. One measures theamount of sample. In practice, however, the analysis is often complicated byinterferences among sample constituents and chemical separations are necessaryto 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 areinterrelated any final choice of analytical method involves compromises and itis impossible to specify a single best method to carry out a given analysis inall laboratories under all conditions. Since analyses are carried out undersmall amounts one must be careful when dealing with heterogeneous materials. Carefullly designed sampling techniques must be used to obtan representativesamples. Preparing solid samples for analysis usually involves grinding to reduceparticle size and ensure homogeneity and drying. Solid samples are weighedusing an accurate analytical balance.
Liquid or gaseous samples are measureedby volume using accurately calibrated glassware or flowmeters. Many, but notall, analyses are carried out on solutions of the sample. Solid samples thatare insoluble in water must be treated chemically to dissolve them without anyloss of analyte. Dissolving intractable substances such as ores, plastics, oranimal tisure is sometimes extremely difficult and time consuming. A most demanding step in many analytical procedures is isolating theanalyte or separating from it those sample constituents that otherwise wouldinterfere with its measurement.
Most of the chemical and physical properties onwhich the final measurement rests are not specific. Consequently, a variety ofseparation methods have been developed to cope with the interference problem. Some common separation methods are precipitation, distillation, extraction intoan immiscible solvent, and various chromatography procedures. Loss of analyteduring separation procedures must be guarded against.
The purpose of allearlier steps in an analysis is to make the final measurement a true indicationof the quantity of analyte in the sample. Many types of final measurement arepossible, including gravimetric and volumetric analysis. Modern analysis usessophisticated instruments to measure a wide variety of optical, electrochemical,and other physical properties of the analyte. Methods of chemical analysis are frequently classified as classical andinstrumental, depending on the techniques and equipment used. Many of themethods currently used are of relatively recent origin and employ sophisticatedinstruments to measure physical properties of molecules, atoms, and ions. Suchinstruments have been made possible by spectacular advances in electronics,including computer and microprocessor development.
Instrumental measurementscan sometimes be carried out without separating the constituents of interestfrom the rest of the sample, but often the instrumental measurement is the finalstep following separation of the samples’s components, frequently by means ofone or another type of chromatography. One of the best instrumental method is various types of spectroscopy. All materials absorb or emit electromagnetic radiation to varying extents,depending of their electronic structure. Therefore, studies of theelectromagnetic spectrum of a material yield scientific information. Manyspectroscopic methods are based upon the exposure of a sample substance toelectromagnetic radiation.
Measurements are then made of how the intensity ofradiation absorbed, emitted,