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Flame Analysis

Flame Analysis

Some forensic analytical determinations rely on the separation of the various components in a mixture of compounds. One means of accomplishing this separation is to heat the sample using a flame.

The separated compounds can then be analyzed and identified. For example, when metals are burned, they can produce a characteristic color. The colors produced by the flame test are compared to known standards and the presence of certain elements in the sample can be confirmed. The color of the flame and its spectrum (component colors) is unique for each element.

Flame analysis or atomic emission spectroscopy (AES) is based on the physical and chemical principle that atomsafter being heated by flamereturn to their normal energy state by giving off the excess energy in the form of light. The frequencies of the light given off are characteristic for each element.

Flame analysis is a qualitative test and not a quantitative test. A qualitative chemical analysis is designed to identify the components of a substance or mixture. Quantitative tests measure the amounts or proportions of the components in a reaction or substance.

The unknown to be subjected to flame analysis is either sprayed into the flame or placed on a thin wire that is then put into the flame. Volatile elements (chlorides) produce intense colors. The yellow color of sodium, for example, can be so intense that it overwhelms other colors. To prevent this, the wire to be coated with the unknown sample is usually dipped in hydrochloric acid and subjected to flame to remove the volatile impurities and sodium.

As useful as it is to forensic analysis, the flame test does not work on all elements. Those that produce a measurable spectrum when subjected to flame include, but are not limited to, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, zinc, and cadmium. Other elements may need hotter flames to produce measurable spectra.

Other forensic analytical techniques are required to identify such substances. Typically, if there is enough of a sample, the sample can be divided into portions for testing by various techniques. This increases the likelihood of properly identifying the components of the sample.

Special techniques are required to properly interpret the results of flame analysis. The colors produced by a potassium flame (pale violet) can usually be observed only with the assistance of glass that can filter out interfering colors. Some colors are similar enough that line spectrum must be examined to make a complete and accurate identification of the unknown substance, or the presence of an identifiable substance in the unknown.

Flame analysis can also be used to determine the presence of metal elements in water by measuring the spectrum produced by the metals exposed to flame. The water is vaporized and then the emissions of the vaporized metals can be analyzed.

see also Analytical instrumentation; Chromatography.

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Flame Analysis

Flame Analysis

Flame tests are useful means of determining the composition of substances. The colors produced by the flame test are compared to known standards. And the presence of certain elements in the sample can be confirmed. The color of the flame and its spectrum (component colors) is unique for each element.

Flame analysis or atomic emission spectroscopy (AES) is based on the physical and chemical principle that atomsafter being heated by flamereturn to their normal energy state by giving off the excess energy in the form of light. The frequencies of the light given off are characteristic for each element.

Flame analysis is a qualitative test and not a quantitative test. A qualitative chemical analysis is designed to identify the components of a substance or mixture. Quantitative tests measure the amounts or proportions of the components in a reaction or substance.

The unknown to be subjected to flame analysis is either sprayed into the flame or placed on a thin wire that is then put into the flame. Volatile elements (chlorides) produce intense colors. The yellow color of sodium, for example, can be so intense that it overwhelms other colors. To prevent this the wire to be coated with the unknown sample is usually dipped in hydrochloric acid and subjected to flame to remove the volatile impurities and sodium.

The flame test does not work on all elements. Those that produce a measurable spectrum when subjected to flame include, but are not limited to, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, zinc, and cadmium. Other elements may need hotter flames to produce measurable spectra.

Special techniques are required to properly interpret the results of flame analysis. The colors produced by a potassium flame (pale violet) can usually be observed only with the assistance of glass that can filter out interfering colors. Some colors are similar enough that line spectrum must be examined to make a complete and accurate identification of the unknown substance, or the presence of an identifiable substance in the unknown.

Flame analysis can also be used to determine the presence of metal elements in water by measuring the spectrum produced by the metals exposed to flame. The water is vaporized and then the emissions of the vaporized metals can be analyzed.

FURTHER READING:

BOOKS:

Broekaert, José. C. Analytic Atomic Spectrometry with Flames and Plasmas. New York: Wiley-VCH Publishing, 2001.

ELECTRONIC:

Helmenstein, Anne Marie. "What You Need To Know About Chemistry-Quantitative Flame Analysis" About, Inc, <http://chemistry.about.com/library/weekly/aa110401a.htm> (March 29, 2003).

SEE ALSO

Air and Water Purification, Security Issues
Chemical and Biological Detection Technologies
Isotopic Analysis
Spectroscopy
Water Supply: Counter-Terrorism

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"Flame Analysis." Encyclopedia of Espionage, Intelligence, and Security. . Encyclopedia.com. 22 Apr. 2018 <http://www.encyclopedia.com>.

"Flame Analysis." Encyclopedia of Espionage, Intelligence, and Security. . Encyclopedia.com. (April 22, 2018). http://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/flame-analysis

"Flame Analysis." Encyclopedia of Espionage, Intelligence, and Security. . Retrieved April 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/flame-analysis

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Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

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American Psychological Association

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Notes:
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  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.