Preparation of biological material for X-ray microanalysis of diffusible elements. I. Rapid freezing of biological tissue in nitrogen slush and preparation of ultrathin frozen sections in the absence of trough liquid.

Any method used for the analysis of diffusible elements within a cell should involve conditions which eliminate the redistribution of those elements. Redistribution of diffusible substances is caused by (a) ice damage during freezing, (b) thawing during sectioning, and (c) thawing during handling of sections. To eliminate this sections were cut (a) in the 5-8 micrometer ice crystal free surface layer obtained by freezing in melting nitrogen, (b) at a specimen temperature of 133 K and a knife temperature of 173 K to 153 K, and the temperature of the chamber was kept low by evaporating nitrogen from an extra reservoir inside the chamber, by regulating the output of a foil heater. A grid carrier was designed to simplify the section collection and the sections were affixed on to the grid in a press assembly. The sections were hard and translucent, and showed faint interference colours.