X‐ray microanalysis of ion distribution in frozen salt/dextran droplets after freeze‐substitution and embedding in anhydrous conditions

Abstract

SummaryA model system using dextran droplets of different salt solutions either frozen together, or sandwiched together after freezing and then freeze‐substituted, embedded and dry sectioned has been investigated by X‐ray microanalysis. X‐ray maps and spot measur ements taken in transects through the interface of both droplets have shown that the P, K and Ca remain well localized in their original droplet. This validates freeze‐substitution as a method for localization of these elements in biological samples. Results with Na were more variable and not always explainable. Success was achieved by the use of super‐dry solvents and maintenance of a dry environment at all stages. We emphasize the need to avoid water contamination not only during freeze‐substitution but also during sectioning, storage and section transfer to the electron microscope.