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Quantitative Analysis

Classical Methods, Instrumental Methods

Quantitative analysis is a chemical analysis performed to find the amount of each component present in a material. It is done by either a classical or instrumental procedure.

A quantitative investigation means that the amount (quantity) or relative amount of each component present is determined. In a pure substance, the entire mass, or 100%, is composed of a single component. In materials composed of two or more substances, a quantitative investigation would determine the mass or relative mass present for each component within the sample. It is not always necessary to find quantitative values for all components that make up a substance. In most cases it is sufficient to analyze the material for one or perhaps more components of interest. The amount of active medicine within an antacid tablet, for example, is significant, whereas the fillers, binders, colorants, and flavoring agents present are of lesser importance.

A quantitative analysis involves more than simply measuring the amount of a component present in a sample

The sample must first be prepared for measurement, usually by placing it in solution if it is not already in soluble form. With complex substances a preliminary separation of the desired component is often necessary to prevent other substances present from interfering with the selected analytical method.

An analyst is one who measures the components of a material quantitatively as a percent or amount present in a sample. Analysts are employed by manufacturing industries to test the reliability of their products. If an automobile manufacturer, for example, specifies that the iron content of the steel used in an automobile is of a certain percentage, then this value must be checked constantly by the manufacturer to see that the automobile meets specifications. This repeated checking is known as quality control and manufacturing facilities have a quality control department employing analytical chemists. Hospitals, too, employ analytical

Method Response
Potentiometry: Many chemical reactions produce electric energy, a battery for example. The amount of chemical to produce a measured potential is calculated.
Coulometry: The amount of electrical current and the duration over which it flows is a measure of the amount of chemical substance producing the current.
Conductimetry: The number of charged chemical components in a solution determine the resistance or conductance of a solution to the passage of electrical current.
Voltammetry: The magnitude of electric potential necessary to cause the breakdown of a chemical substance and the current resulting from that breakdown are related to the amount of chemical present.
Ultraviolet, visible, infrared, and x-ray spectometry: The extent to which these rays are absorbed by a sample depends upon the amount of sample present
Thermogravimetry: The loss in weight of a substance as it decomposes upon heating is proportional to the amount of substance initially present.
Nuclear magnetic resonance: For chemicals showing magnetic properties the strength of the magnetism is related to the amount of substance present.
Nuclear activation analysis: The amount of radioactivity produced by a substance is proportional to the amount of material emitting radiation.
Mass spectrometry: The intensity of each component fraction present as a chemical is broken apart relates to the amount initially present.

chemists to test patients for proper amounts of medication. Athletes are subjected to quantitative testing to determine the presence and amount of possible illicit drugs in their bodies. The federal government carries out frequent quantitative measurements of environmental samples. Should, for example, a company generate greater amounts of a pollutant than is allowed by law, then the government can fine the company or force it to close until it meets government regulations. Legislators at the local, state and national level use quantitative results to formulate laws that prevent the general public from coming into contact with dangerous amounts of harmful chemicals in food, medicine, the environment, and other areas.

Various methods are employed to undertake a quantitative investigation. These methods are broadly classified as classical and instrumental methods.

Additional topics

Science EncyclopediaScience & Philosophy: Propagation to Quantum electrodynamics (QED)