Fluoride spectrophotometric procedure

The spectrophotometric procedure with alizarin complexone is the most widely used method for the determination of fluoride in seawater. Small modifications have been made to the method first proposed by Greenhalgh and Riley (1961). 

The method for the determination of fluorine is based on decomposition of the sample by oxygen flask combustion, followed by spectrophotometric determination of the fluoride produced by a spectrophotometric procedure involving the reaction with the cerium(III) complex of alizarin complexan (1,2-dihydroxy-anthraquinone 2-ylmethyl-amine N,N-diacetic acid). The blue colour of the fluoride containing complex (absorption maximum, 565 nm) is completely distinguishable from either the yellow of the free dye (maximum absorption, 423 nm) or the red of its cerium(III) chelate (maximum absorption, 495 nm). 

Fluoride Determine as directed in Method III under Fluoride Limit Test, Appendix IIIB, except in the Procedure, use 10 mL of 1 N hydrochloric acid to dissolve the sample. Lead Determine as directed in the Flame Atomic Absorption Spectrophotometric Method under Lead Limit Test, Appendix IIIB, using a 10-g sample. 

Fluoride can be determined with three significant figures using a fluoride electrode. Otherwise, the recommended procedure is a spectrophotometric determination with lanthanum alizarin complexone. 

A spectrophotometric method was worked out by Wang and coworkers [53] for the determination of trace level fluoride concentration of water samples. In this procedure, the samples are mixed with a reagent mixture (alizarin-3-methylimino-N,N-diacetic acid/ sodium acetate/12.5% acetic acid buffer of pH 4.1/1 mM lanthanum nitrate (1 1 1 )). After a reaction time the colored complex is extracted with 5% N,N-dimethylaniline solution in 3-methylbutan-l-ol and the absorbance is detected in a special, long capillary at 580 nm. 

Absorption spectrophotometric analysis procedures have been developed for a number of environmental species. For water contaminants alone, these include procedures for the determination of arsenic, boron, bromide ion, cyanide, fluoride, nitrate, phenols, phosphate, selenium, sUica, sulfide, surfactants, and tannin and lignin. A typical such procedure is the spectrophotometric determination of phenol in water by the reaction with 4-aminoantipyrene... 

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