DETERMINATION OF LABILE-IONIC AND TOTAL FLUORINE IN HUMAN DIETS BY GRAPHITE-FURNACE MOLECULAR ABSORPTION SPECTROMETRY WITH MICRODIFFUSION AND OXYGEN FLASK COMBUSTION MINERALIZATION

Flourine was determined in human diets from different countries by the formation of the diatomic molecule aluminium monofluoride in an electrothermal graphite furnace and measurement of the molecular absorption band at 227.45 nm. The labile-ionic fluoride fraction was measured by microdiffusion of unashed diets, using HClO4 + AgClO4, and total fluoride was estimated by oxygen flask combustion, using Al+3 + Sr+2 as absorbent solution. Both methods yielded recoveries higher than 90 %, and precision better than 10 %. The detection limit is about 0.05-mu-g/g for oxygen flask combustion and about 0.1-mu-g/g for microdiffusion. The two methods gave considerablely different fluoride contents in some diets; this can be attributed to the fluoride that is linked to organic matter (organic fluoride).