Non-freezing techniques of preparing biological specimens for electron microprobe X-ray microanalysis.

In this paper a review is presented of the many ways the fluids involved in conventional wet chemical E.M. preparative techniques (including precipitation procedures) disturb the in vivo chemical integrity of biological tissues. The artifacts discussed are: (i) bulk element loss, (ii) phase transformations in mineralized tissues, (iii) redistribution of endogenous tissue elements; (iv) introduction of extraneous elements. Finally, the range of biological applications to which wet chemical methods have been successfully applied by various authors is briefly discussed to provide a realistic working perspective. It is stressed that in most of these applications the authors restrict themselves to a comparison of the chemistry of cells or their constituent organelle systems and do not attempt to define the in vivo chemical composition of cells. The author concludes that since all preparative procedures available to the microprobe analyst suffer from some form of restrictive compromise, it may not be advisable to think of a general microprobe preparative technique but, alternatively to apply different preparative techniques according to the specific biological answers sought.