The technique of X-ray microanalysis has existed for considerably longer than is, perhaps, generally realised, having been invented in 1951 and first applied to biological material at the beginning of the 1960s (Hall, 1986). Much very useful pioneering work was carried out using wavelength-dispersive detectors. However, there can be no doubt that the introduction of the energy-dispersive detector based on the Si(Li) detector crystal, with its capability of multi-element analysis, and ease of operation led to the technique becoming more widely accepted. For the detection of the majority of elements the ease of use of the EDS detector offsets its lower resolution, and both the continued improvements in the Si(Li) detectors and the introduction of germanium detectors, will help to improve the sensitivity of the technique.

Biological specimens are many and varied with their own special problems for quantification, and perhaps the second most important development in X-ray microanalysis for biologists has been the commercial availability of software for carrying out quantitative routines. The procedure most commonly used for quantification is the continuum normalisation method of Hall (Hall, 1971). With the advent of the microcomputer in the early 1980s the first software for applying the Hall technique to biological specimens became available, and now the importance of quantification of spectra from biological specimens is recognised with all major detector manufacturers offering this option with their software.