flame test

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flame photometry (flame spectrometry) A technique analogous to emission spectrometry, but using a flame to excite electrons, rather than an arc or plasma. It is a simple and straight forward analytical technique that is basically a quantitative version of a ‘flame test’. A known weight of sample is dissolved in hydrofluoric acid and either perchloric or sulphuric acids, portions of the solution are added to a flame, and the strength of emission of light of a particular wavelength produced by the potassium in the flame is recorded. This is then compared with those produced by standard solutions. The final results may be affected by sodium concentrations as well as by the sulphuric acid. Perchloric acid, iron, magnesium, aluminium, and calcium also interfere with the potassium emission but their effects may be reduced by buffering and by the removal of interfering ions.

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flame test, test used in the identification of certain metals. It is based on the observation that light emitted by any element gives a unique spectrum when passed through a spectroscope. When a salt of the metal is introduced into a Bunsen burner flame, the metallic ion produces characteristic color in the flame. Some metals and the colors they produce are: barium, yellow-green; calcium, red-orange; copper salts (except halides), emerald green; copper halides or other copper salts moistened with hydrochloric acid, blue-green; lithium, crimson; potassium, violet; sodium, yellow; and strontium, scarlet. The value of this simple flame test is limited by interferences (e.g., the barium flame masks calcium, lithium, or strontium) and by ambiguities (e.g., rubidium and cesium produce the same color as potassium). A colored glass is sometimes used to filter out light from one metal; for instance, blue cobalt glass filters out the yellow of sodium.