The use of tetrahydroxyflavanol, morin, for the identification of aluminium by the formation of a green fluorescent inner complex salt is well knownlj 2, and has been applied to the detection of gallium, scandium, beryllium and zinc3. FEIGL has recorded a more sensitive modification of the test on paperr.
In searching for a test for aluminium in the presence of vanadium, it was observed that the morin reaction failed, even at relatively high aluminium concentrations. This was attributed to complex formation analogous to the action of phosphate ion, which was confirmed by suppression of the fluorescence in the presence of phosphate. It was thought that this might provide a means of identifying or detecting such anions, and an investigation was conducted to ascertain a), which anions interfered with the morin reactions and would have to be removed before testing for the cations, and b), which anions were suitable for detection by virtue of their interference.
In daylight, the aluminium test on paper has about the same sensitivity (0.3 r) as that on a spot plate: under ultra-violet, it is greater, but not as high as that quoted by FEIGL (0.005 r). This is probably due to a difference in intensity of the ultra-violet source used.