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II. Reading1

Analytical chemistry

Analytical chemistry is the branch of chemistry that deals with determining the identity and concentration of chemical substances (analytes). Analytical chemistry can be divided into subdisciplines based on the type of samples that are analyzed: atomic, molecular, or biological. Atomic analysis involves the identification and quantification of elements that often occur in complex mixtures. Analytical chemists are often asked to find the concentration of manganese in a steel sample, for example. Molecular analysis involves the identification and determination of molecules.

Analytical chemistry has significant overlap with other branches of chemistry, especially those that are focused on a certain broad class of chemicals, such as organic chemistry, inorganic chemistry or biochemistry. Analytical chemistry and experimental physical chemistry have a unique relationship in the tools used in experiments. Analytical chemists use a variety of chemical and physical methods to determine identity and concentration. Purely chemical methods were developed in the nineteenth century and therefore are called classical methods. Physical methods involve determinations based on the amount of light absorbed or emitted by the analyte or on the strength of an electrical signal created by the analyte at an electrode.

Classical methods or quantitative analyses include gravimetry, where the amount of a substance is determined by the mass of product generated by a chemical reaction, and titrimetry, where concentration is determined by the volume of a reagent needed to completely react with the analyte. These methods are highly accurate and precise but require a sufficient amount of sample, and a concentration of analyte in the sample of at least 0.1 percent. Furthermore these analyses require the constant attention of a trained scientist. Most modern analytical chemistry techniques are based on instrumental methods involving optical and electrical instruments. Elemental concentrations can be determined by measuring the amount of light absorbed or emitted by gas-phase atoms. Similarly, molecular concentrations are correlated with the emission or absorption of light by molecules in aqueous solutions. Electrodes, like the glass pH electrode, measure the electrical potential due to the presence of specific ions in solution. Spectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, and so on. Finally, chromatographic methods separate the components of complex mixtures to determine the concentration of each component.

Research is under way to develop techniques that can determine the presence of one atom or molecule in solution, to reduce the size of the instrumentation required, and to analyze the contents of a single cell. These new techniques hopefully will enable the early detection of disease, the remote sensing of a chemical spill, or the rapid analysis of water and air on space vehicles.

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