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• Analytical chemistry is applied throughout industry, medicine, and all the sciences.
• The concentrations of oxygen and of carbon dioxide are determined in millions of blood samples every day and used to diagnose and treat illnesses.
• Quantities of hydrocarbons, nitrogen oxides, and carbon monoxide present in automobile exhaust gases are measured to determine the effectiveness of emission-control devices.
• Quantitative measurements of ionized calcium in blood serum help diagnose parathyroid disease in humans.
• Quantitative determination of nitrogen in foods establishes their protein content and thus their nutritional value.
• Analysis of steel during its production permits adjustment in the concentrations of such elements as carbon, nickel, and chromium to achieve a desired strength, hardness, corrosion resistance, and ductility.
• The mercaptan content of household gas supplies is monitored continually to ensure that the gas has a sufficiently obnoxious odor to warn of dangerous leaks.
• Farmers tailor fertilization and irrigation schedules to meet changing plant needs during the growing season, gauging these needs from quantitative analyses of plants and soil.
• The selected method usually represents a compromise between the accuracy required and the time and money available for the analysis.
• Sampling is the process of collecting a small mass of a material whose composition accurately represents the bulk of the material being sampled.
• High reliability in analysis often requires a large investment of time.
• The number of samples to be analyzed influences the choice of method to some degree.
• The complexity of the sample and the number of components in the sample always influence the choice of method to some degree.
• Many sampling problems are easier to solve than the two just described.
• The second step in a quantitative analysis is to acquire the sample.
• Sampling is also a problem in biological systems, as the concentration of analytes in a specimen depends on a variety of physiological and environmental variables.
• Strict procedures have been developed for sampling and transporting specimens to the clinical laboratory to ensure that the sample is representative of the patient at the time it is collected and that its integrity is preserved until the sample can be analyzed.
• The composition of the sample must be representative of the bulk of material from which it was taken.
• Sampling is a difficult undertaking that requires a careful, systematic manipulation of the entire shipment when the bulk is large and heterogeneous.
• Quantitative analytical measurements also play a vital role in many research areas in chemistry, biochemistry, biology, geology, physics, and the other sciences.
• Calibration methods are discussed in detail in Chapter 8.
• Computing analyte concentrations from experimental data is usually relatively easy, particularly with computers.
• Replicate samples are portions of a material of approximately the same size that are carried through an analytical procedure at the same time and in the same way.
• Gravimetric methods, discussed in Chapter 12, and coulometric methods, considered in Chapter 22, do not require the determination of the proportionality constant.
• In the determination of manganese in steel, the element must be oxidized to MnO 4 2 before the absorbance of the colored solution is measured.
• Quantitative measurements of potassium, calcium, and sodium ions in the body fluids of animals permit physiologists to study the role these ions play in nerve-signal conduction as well as muscle contraction and relaxation.
• All analytical results depend on a final measurement of a physical or chemical property of the analyte, which must vary in a known and reproducible way with the concentration of the analyte.
• If the sample does not have a property that is proportional to analyte concentration, other chemical steps may be necessary to convert the analyte to a form suitable for measurement.
• Once the analyte is made soluble, the next step is to determine if the sample has a property that is proportional to analyte concentration and that can be measured.
• Eliminating interferences in an analysis involves isolating the analytes from interferences before the final measurement is made.
• The experimenter must provide some measure of the uncertainties associated with computed results if the data are to have any value.
• Calibration is the process of determining the proportionality between analyte concentration and a measured quantity.
• Chemists unravel the mechanisms of chemical reactions through reaction rate studies.
• The rate of consumption of reactants or formation of products in a chemical reaction can be calculated from quantitative measurements made at precise time intervals.
• Materials scientists rely heavily on quantitative analyses of crystalline germanium and silicon in their studies of semiconductor devices whose impurities lie in the concentration range of 1 3 10 2 6 to 1 3 10 2 9 percent.
• In a volumetric method, the volume of a solution containing sufficient reagent to react completely with the analyte is measured.
• In a group of miscellaneous methods, measurements are made of such quantities as mass-to-charge ratio of ions by mass spectrometry, rate of radioactive decay, heat of reaction, rate of reaction, sample thermal conductivity, optical activity, and refractive index.
• Analytical methods are classified according to the nature of this final measurement.
• In electroanalytical methods, electrical properties such as potential, current, resistance, and quantity of electrical charge are measured.
• The interdisciplinary nature of chemical analysis makes it a vital tool in medical, industrial, government, and academic laboratories throughout the world.