Diffusible ion localization by ion microscopy: a comparison of chemically prepared and fast-frozen, freeze-dried,...

The necessity of low temperature preparative procedures for diffusible ion localization using the ion microscope has been established with rat liver as the test material. Using conventional fixation procedures, significant ion loss and redistribution were observed which exceeded the 1 micrometer lateral resolution of the direct imaging ion microanalyser. The compositional morphology evidenced in chemically prepared versus fast-frozen, freeze-dried, unfixed material was compared and evaluated in terms of ion retention, ion redistribution and morphological integrity. A mass spectral analysis of both preparations has been presented and discussed with regard to spectral interferences and elemental sensitivities. Ion images of sodium and potassium were recorded for chemically prepared liver sections and compared with the ion distributions obtained for unfixed, fast-frozen, freeze-dried 1 micrometer thick sections. The magnitude of ion loss during preparation of samples removed at different stages in the course of chemical processing was determined by atomic absorption and flame emission spectrophotometry.