title: Biological X-ray microanalysis.
abstract: By means of X-ray microanalysis it is now practical to detect approximately 10(-19) g of an element in a static-probe analysis within an ultrathin section, with analytical spatial resolution in the range 20--30 nm. The main difficulties for biological microanalysis are connected not with sensitivity but with specimen preparation and beam damage. Careful cryopreparation, beginning with the quench-freezing of a small block of tissue, is essential even for determining the storage sites, or sites of binding in vivo, of physiologically active elements. In frozen-dried or frozen-hydrated sections of quench-frozen tissue, it is now possible to measure local mass fractions of diffusible as well as of bound elements.
mesh_terms: D001695:Biology; D004577:Electron Probe Microanalysis / Q000379:methods*; D005404:Fixatives; D005615:Freezing; D007089:Image Enhancement; D008854:Microscopy, Electron / Q000379:methods*; D008903:Minerals / Q000032:analysis; D013194:Staining and Labeling
chemical_list: D005404:Fixatives; D008903:Minerals