Gravimetric Determination of Aluminium

8 Hydroxyquinoline is a chelating ligand (referred to as oxine) which forms insoluble complexes with a number of di- and trivalent metals. The oxinates of these metals contain 2 or 3 oxinate groups per metal ion. In the case of aluminium the complex has 3 chelating ligands. Complete precipitation takes place at pH values of 5-10. 

Strips for the approximate determination of low concentrations of aluminium are available commercially. The colour produced by a reagent in the strip, when immersed in an [Ap ] 10-250 ppm, is a semiquantitative test for the ion. 

1 Fluorescence of 8-l droxyquinoline (oxine) and its complex with AI When a solution of oxine in ethanol is irradiated with a medium pressure mercury lamp, it emits fluorescence with a broad maximum at 429 nm. When the solution is made acidic or alkaline, the maxima shift to longer wavelengths. A shift to longer wavelengths 

Prepare a concentrated solution of oxine in ethanol. Expose it to a medium pressure mercury lamp and observe the fluorescence. If a spectrofluorometer is available, measure the intensity of the emission at 430 nm. Saturate ethanol with the precipitate obtained in the gravimetric method and carry out the same procedure on the solution. If possible measure at 490 nm. 

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