The mineral concentration of the body is determined by weighing a sample before and after heating to a very high temperature to convert complex molecules to individual elements. The carbon, nitrogen, oxygen, etc. are volatilized, leaving the heavier mineral elements, i.e., the ash. A fat-free sample is generally used. Although there are minerals in every cell in the body, the bulk of the mineral content is derived from the skeleton. Thus, the ash concentration is used to represent the skeletal mass.
Individual minerals may be determined on the ash sample. Generally, atomic absorption methods are used, but specialized chemical methods are available for some elements. Whole-body techniques using detection of natural radiation from particular elements, e.g., 40K, or elements made radioactive by neutron activation are available.
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