Alumina-types present striking differences in physical properties, which have detrimental effects on accuracy of spectrochemical analysis. Calcination with a small amount of aluminium fluoride eliminates many of these differences. The "mineralized calcination step" converts all samples to essentially alpha alumina of very similar monocrystal size, and subsequent grinding while mixing with graphite introduces still more uniformity. This treatment is simple and can be carried out on a number of samples at the same time. It provides significant improvement in both accuracy and precision. Details of the pre-treatment are presented along with analytical data to show the improvement.
P. E. Lemieux, "Improved Spectrochemical Analysis of Alumina By Mineralized Calcination," Appl. Spectrosc. 17, 153-155 (1963)