Extractive photometric determination of gallium with 8-quinolinol in layered crystals of bismuth telluride-estimation of the determination limit

A method for determining microgram amounts of gallium in milligram samples of layered monocrystals of the type A(V)(2)B(VI)(3) is described. For the separation of 1-5 mug of gallium(III) from a large excess of bismuth in a single extraction the recommended conditions are pH 3.6-4.2 (acetate buffer, V(aq) 40 ml), an adequate excess of 8-quinolinol for complete extraction and of thiosulphate for masking bismuth. The absorbance of a chloroform extract (V(org) = 10 ml) is measured at 392.5 nm in a 50-mm cell against a blank extract concurrently obtained with a solution of pure Bi(2)Te(3). Reference polycrystalline materials are used to check the precision and accuracy of the method. In routine analysis of layered monocrystals a relative standard deviation of 4-8% is to be expected for about 1 mug of gallium in the extraction system. Estimation of the limit of determination, based on two statistical models, is discussed with respect to the error of the method and the fluctuation of the blank.