X-ray microanalysis with continuous specimen cooling: is it necessary?

An X-ray microanalytical preparation technique using continuous specimen cooling and consisting of cryotransfer of frozen sections into the electron microscope, freeze-drying of the sections within the microscope and analysis at liquid nitrogen temperature is compared with a more conventional technique characterized by freeze-drying of sections in a vacuum evaporator with subsequent carbon coating, transfer of frozen-dried sections through the room air into the electron microscope and analysis at ambient temperature. For this comparison elemental concentrations in mitochondria, in areas of the rough endoplasmic reticulum and in the cytoplasm of rat hepatocytes, were measured. Si is found in abundance in specimens freeze-dried outside the microscope due to the use of a vacuum evaporator contaminated with pump oil. Radiation damage will be more severe at ambient temperature and is assumed to be the reason for observed differences in S concentration in mitochondria and the cytoplasm. However, peak-to-background ratios for Na, Mg, P, Cl and K are in general the same for both types of preparation.