X-RAY-MICROANALYSIS OF ION DISTRIBUTION IN FROZEN SALT DEXTRAN DROPLETS AFTER FREEZE-SUBSTITUTION AND EMBEDDING IN ANHYDROUS CONDITIONS

A model system using dextran droplets of different salt solutions eith er frozen together, or sandwiched together after freezing and then fre eze-substituted, embedded and dry sectioned has been investigated by X -ray microanalysis, X-ray maps and spot measurements taken in transect s through the interface of both droplets have shown that the P, K and Ca remain well localized in their original droplet, This validates fre eze-substitution as a method for localization of these elements in bio logical samples, Results with Na were more variable and not always exp lainable. Success was achieved by the use of super-dry solvents and ma intenance of a dry environment at all stages. We emphasize the need to avoid water contamination not only during freeze-substitution but als o during sectioning, storage and section transfer to the electron micr oscope.