X-ray microanalysis has become increasingly used to study the elemental composition of biological specimens and has provided valuable information on the identity and occurrence of diffusible and bound ions, inorganic deposits and elements that are structural components of macromolecules. The attractions of X-ray microanalysis to the potential investigator in terms of spatial resolution and range of elements that can be detected have already been mentioned in Section A. The analytical sensitivity in terms of minimal detectable mass (10−19 g) also presents considerable opportunity to the analyst, though the value for sensitivity on a mass fraction basis (normally no better than 0.1 % with energy dispersive systems) poses major limitations.

The diversity of applications can be considered both in terms of general areas of study and type of specimen examined.

Applications of X-ray microanalysis to different subject areas of biology

X-ray microanalysis has been used in a variety of disciplines within biology, as exemplified by the range of chapters in this section of the book. These areas include microbiology, plant biology, animal biology (vertebrate and invertebrate tissues, cultured animal cells), medicine and environmental biology. A computer survey of the relative numbers of papers in these different areas (Table D1) indicates a clear preponderance in the spheres of animal biology and medicine.

The role of X-ray microanalysis in human physiology and medical research has recently been reviewed by Shelburne et al. (1989), and is important in the study of aspects such as the activity of Ca in cellular processes, ion transport in epithelia and the possible importance of cations in mitogenesis and oncogenesis.