The determination of wet weight concentrations of elements in freeze-dried cryosections from biological cells.

Energy dispersive X-ray microanalysis in STEM (scanning transmission electron microscope) of freeze-dried cryosections from biological cells provides information on the subcellular element distribution in terms of dry weight concentration. The local dry weight content in the range of 5-50%, respectively the local water content within 50 to 95%, in different subcellular compartments can be determined by measuring the darkfield intensity by means of an annular detector in STEM. Calibration is done by measuring the darkfield intensity of similarly prepared cryosections from dextran-water-solutions in varying concentration. Thus, by combining the X-ray microanalytical data evaluated by the continuum method with the STEM darkfield values, wet weight concentrations of elements in subcellular compartments are obtained. The method was applied to fibroblast cells in suspension. The reliability of this method is compared with other techniques to measure mass and intracellular water by electron microscope methods.