Secondary ion microanalysis of fluorine in apatites of biological interest.

A Cameca IMS 300 ion analyzer has been used to measure fluorine concentrations in tooth material. Samples of human and shark teeth were studied. Negative oxygen primary ions produce secondary mass spectra in which positive as well as negative fluorine ion peaks are well re­ presented. With constant measuring conditions, the reproducibility of the F/Ca ion ratios is satis­ factory. Fluorine concentrations in the 10 ppm region are easily recorded. By means of samples previously measured by macroscopic F-determining methods, a calibration can be effected to ob­ tain, from the ion current ratios, at least semiquantitative values of F-concentrations. In a sample of human enamel, the F-concentration was found to vary from about 3000 ppm at the surface to about 100 ppm in the interior. In shark enamel the composition at the surface cor­ responded to nearly saturated fluorapatite, 3.6% F, but the fluorine concentration decreased distinctly at increasing depth.